The poem begins with an unnamed speaker introducing an old document, written in Greek, that was found in the "Chosen Chest" and attributed to Pamphylax. The speaker notes that he awaits "His coming" (the person to whom "His" refers is not identified) and then begins to share the contents of the document.
The parchment begins with its narrator (presumably Pamphylax) making arrangements for a dying man. He and several others have been taking care of this fugitive, hiding him in a desert cave while a simple Persian man stands guard outside. Pamphylax and the other disciples of the dying man feed him wine, but cannot awaken him. Suddenly, one of their companions, a boy, fetches a book from the desert and then reads from it a line attributed to the Gospel of John: "I am the Resurrection and the Life."
The old man wakes, and we soon realize that this is the author of that Gospel, St. John himself. He begins to speak, and most of the poem following the text is from his own dictation. John admits he is out of sorts and feverish and has trouble knowing for certain who, where, and when he is.
Pamphylax interrupts John's speech to explain John's doctrine, which is reflected in his Gospel. As explained, John understands man as separated into three levels: body, mind, and soul. While the soul is obviously the highest expression of man and closest to heaven, all three interact to lend credence to one another as a unified whole. The body's ability for physical perception is necessary to give content to the mind that can then be fed to the soul for the purpose of "constituting man's self."
John continues his dictation, in which he addresses questions of truth. He notes that he is the sole survivor of those who knew the "Word of Life" (he rarely mentions Christ by name), and that he spent his life "bidden to teach" love. For a long while, men believed his testimony, but later, he was instructed by God to "take a book and write," and so he penned his Gospel. He continued thereafter to teach the truth of love, but after a while, men began to doubt both the veracity of his Gospel and even whether he was actually the John who knew Christ. These doubts were compounded by the world's insistence on knowing specifically when Christ would return. When John fell sick, his disciples brought him to the desert to escape the doubters, and here he now lies.
He lashes out at those who need empirical evidence to believe in God and love. John believes that evidence of love and God is everywhere in our lives, in the way that "truth, breaking bounds, o'erfloods [his] soul." Where some need "plain historic fact, Diminished into clearness" in order to believe truth, John believes the "soul learns diversely from the flesh" and can intuit love in everyday life. Using the example of how fire brings reprieve from bitter cold, he argues that the body can deliver to the soul evidence of wonder and love, so that the body and soul both have a part to play in establishing a person's faith.
However, as time has passed since Christ's death, mankind has begun to seek new proofs. John argues that "To test man, the proofs shift," and that the journey towards faith must require the individual to be complicit. In other words, one cannot count on Christ-like miracles any more, but instead must find that faith in himself and his own world. We must always search.
John acknowledges the accusation of his doubters, who claim he was not actually at Christ's crucifixion as he claims in his Gospel. He admits it was indeed a lie, but a defensible lie, since through his falsehood he was able to communicate the greater truth of Christ's love to others. He blames the accusation on the world's extreme emphasis on material fact over spirit. He is especially bothered because the power of Christ is very much "the mere projection from man's inmost mind," but people are more inclined to look outside themselves than inside for validation.
He thinks of how man has always turned to gods, suggesting that man invents these gods and that they evolve with man's needs, but again, that the current stage in history makes this impossible since people want only material fact. He argues that "man was made to grow, not stop" and as such ought to be able to elucidate Christ's message in himself, rather than relying on easy miracles for proof. He admits that he did invent a miracle in his Gospel, but again argues that he did so in service of a greater truth that was communicated through his lie. Further, he acknowledges that the choice to stage only a few miracles was a practical decision, and that too many miracles would "compel, not help" since man's faith has already been established. His hope was that from that initial faith, man's prowess would grow, but instead man's focus on reason has led to "ignorance."
Towards the end of his speech, John does acknowledge that man cannot reach perfection, but refuses to allow this as an excuse to compromise the search for knowledge and truth. Even though "what he considers that he knows to-day… he will find misknown [tomorrow]," John believes it is part of man's higher faculty to constantly seek greater truths. "God's gift was that man should conceive of truth/And yearn to gain it."
In the midst of these ideas, John dies and the speaker explains how they buried him and how he alone would survive to document this final philosophy from his master. He hopes that those who read his words will follow John's teachings.
The poem ends with the original speaker again interjecting that another man, Cerinthus, added an addendum to the parchment from which this piece has been taken. The addendum notes that even if Christ's return is delayed by another 12 years, there are many who will grieve while others will merely allow Christ to be made manifest in themselves.
There were contemporary critics of Browning who accused him of being less a poet and more a philosopher, and "A Death in the Desert" could certainly be used to support this claim. Its primary message seems to be a doctrine concerning man's pursuit of truth and the connection between material perception and the transcendent spirit.
Of course, Browning is never one to subscribe to any fixed philosophy, and in fact, his work suggests overall less the acceptance of a creed than that, as John says, "What [man] considers that he knows to-day, Come but to-morrow, he will find misknown." So it is best to understand this poem as one of Browning's many dramatic monologues, in which he takes the voice of a particular individual in order to explore questions of universal humanity.
The main conflict at work here is faith vs. reason. Typically, this discussion gets broken into a strict dichotomy – a person can either trust in 'faith,' at which point he is spiritual and relies on intuition, emotion, and visceral reactions, or in 'reason,' at which point he relies on his own perceptions and mental understanding of them. John posits the ultimate goal for man as "love," and the question is whether one is better equipped to achieve heavenly love with faith or with reason.
The basic tenant of John's philosophy is that faith and reason should not be so strictly separated. He laments a world in which reason has triumphed at the expense of faith and spirit. His physical dilemma is a symptom of that: his teachings and the validity of his Gospel have been called into question, and so his followers have had to hide him in the desert while he dies. They place a Persian man (a "Bactrian") as guard, suggesting that John's doubters are intense in their desire to have him punished or at least apprehended. What they accuse him of is not only falsifying information about Christ's life, but also of using the life of Christ to his own ends. What saddens John is that people in his day and age only wish to understand Christ through physical details and confirmed reports, while ignoring the larger spiritual truth behind him.
A bit of history can help to understand these charges. Browning was inspired to write this poem after reading Ernest Renan's Life of Jesus, translated to English in 1863, which called into question the validity of John's Gospel. It is well-accepted that John lived later than Jesus, and indeed, of the four Gospels (the first four books of the New Testament), John's is the most philosophical and ideological. He speaks of Christ in terms of concepts ("the way," "the life," etc.), with less emphasis on Christ as a living, breathing human being. However, Browning likely was concerned not with countering Renan's claims on John, but with exploring his own Victorian society, which had gone through the Enlightenment period and viewed the faculty of reason as man's best tool towards understanding the world's truth. The sheer intellectual content of this poem is enough evidence that Browning is not a hard-lined Romantic who eschews reason, but he does believe that a strict adherence to it alone leads man to recede, and ironically negates the progress of the Enlightenment. As John says, "This is death and the sole death,/When a man's loss comes from his gain,/Darkness from light, from knowledge ignorance,/And lack of love from love made manifest." The Enlightenment opened to man a new world of perception, but Browning fears that it has shut off from man his greater faculties. Where mankind ought to use reason as a new tool towards truth, the Enlightened man, it could be argued, has identified reason as the end in itself and hence stopped seeking the greater truth.
So Browning's point, as espoused through John, is that the strict separation of reason and faith is fallacious. Instead, as it traced in the unnamed speaker's interruption made early in the poem, John's philosophy is that we are made of three faculties: body, mind, and spirit, and all three are interdependent of one another. That soul is the greatest does not mean that soul can reach truth without the physical perceptions given by the body. This is at its core an Aristotelian concept, later clarified by Immanuel Kant, that our greatest concepts and love need physical perception in order to be given shape.
John has constructed his life and legacy under this philosophy. For him, the end goal was love, and he was willing to make whatever choices facilitated the reaching of that goal. Therefore, he admits he did create in his Gospel a miracle and that he lied about having been at the Crucifixion. For him, these white lies merely provided physical shapes that would allow future Christians to transcend to mind and then spirit, ultimately coming closer to God's love. He is accused, therefore, of crimes he is admittedly guilty of, but his point is that his actions were not crimes, but rather forgivable, virtuous decisions. He argues that we ought to have our faith in the thing we are pursuing ("love"), not in the report of the thing (whether the miracle he described actually happened or not). In fact, he argues that Christians in his day should not need miracles any more – the early miracles were enough to set the spark for faith in God and love, and now man's faculties are capable of continuing the search without having to have such physical validation.
In all of this is a contemplation of subjective vs. objective truths. John's ultimate goal is to lead others to the objectivity of God's love, which lies above our personal, subjective perceptions. However, he does not doubt that the search itself is necessarily subjective since it relies on our own limited perspectives. Again, the general approach to this question is that they are mutually exclusive, and this poem fits within Browning's oeuvre in suggesting that the two need not cancel one another out. If Browning wants to take a very specific voice (i.e., that of the duke in "My Last Duchess,"), that does not mean he is incapable of speaking objective truth through that voice, or of expressing his own subjective fascinations thereby.
So in a way, this poem is as much about the artist as it is about religion. It's telling that Christ is mentioned very few times in a poem about one of his main archivists. John is far more taken with the concept of "love" than he is in the particulars of Jesus Christ himself, and in fact gives respect to the Greek religions that preceded Christianity, since those too were a step in man's search for truth. John suggests that "God's gift was that man should conceive of truth/And yearn to gain it," meaning that his goal is not to reveal a 'secret' to man, but rather to help man continue that never-ending struggle towards perfection. That we are imperfect and doomed to fail in this quest does not negate the virtue of trying, which is very much Browning's credo on art. Art is about exploring the human condition, telling lies (making up stories) to reveal the greater truth, and those who see it solely as a "lie" are missing the point: lies and truths are both part of the same struggle to get to a deeper reality. Defining 'truth' as "what actually happened" leads only to a sad, scared life. Indeed, John speaks with pity of those who live in fear, constantly worried about when Christ will return, so stuck on that dogma that they have missed God's bigger message, which is that we should constantly struggle in pursuit of love.
The framing device also suggests that the poem can be viewed as a comment on the artist. The main speaker, at the beginning and end, never identifies himself but is instead an archivist of John's life and philosophy, much as John was for Christ through the writing of his Gospel. And yet the unnamed speaker takes license with his account by adding an addendum spoken by Cerinthus, suggesting that he has provided context to interpret John's words (rather than letting John simply speak for himself). The struggle towards truth is constant progress – John calls progress "man's distinctive spark alone" – towards truth, but progress requires us never to accept anything as true, but rather to constantly reinterpret everything. By using this framing device, Browning shows us that John's words themselves are merely one further step that needs be appropriated and reinterpreted, lest we otherwise lie down and stop trying. This is what the Christians John criticizes have done – they have stopped searching and now wait sadly for Christ's return, whereas he believes they ought to continue pushing forward, reinterpreting Christ through the generations so as to grow stronger. What matters most is the truth; what matters least is the author. So just as John was willing to make up facts about Christ to get to truth, so does this unnamed author add details to John's life to get to his truth, and so by default is Browning reinterpreting this man's work to suggest his own truth.
In the end, though, Browning is too interesting a monologist to make this solely a piece about philosophy, and indeed John's character does constantly reveal itself. John is easy to identify as a megalomaniac in himself, which adds fascinating dramatic irony. Like any proclaimed prophet, he survives through the support of disciples, and the length and rambling nature of his speech gives it a sense of raving that can be enjoyed for its extremity even as the content is thought-provoking. In his discussion of the miracles he invented, one notices the shrewdness with which he has constructed this philosophy. He admits he invented the miracles for a greater good (as discussed above), but also that he stopped inventing miracles because too many would make man dependent on them. The shrewdness of this thought process reveals that he, like all leaders, was willing to manipulate his public to achieve his desired effect, and so even if the effect is defensible, there's an extent to which he is still a liar. By speaking in his voice (and using the framing device), Browning is free from directly weighing in on whether such lies are defensible, instead allowing us to consider both sides of the question.