In the Interlude, the Archbishop preaches in the cathedral on Christmas morning, 1170. He delivers the entire speech, and there are no stage directions. The Interlude begins with a verse from Luke praising God, after which Thomas promises his sermon will be short. He announces that his intention in the sermon will be to explore the "deep meaning and mystery of our masses of Christmas Day." He notes how there is a contradiction in these masses – they exist both to celebrate Christ's birth and to celebrate his death. It is strange, Thomas notes, "for who in the World will both mourn and rejoice at once and for the same reason?" (198).
Thomas wishes to reflect on the meaning of the word "peace." He notes how Christ told his disciples, "My peace I leave with you, my peace I give unto you" (198). By analyzing the context of both Christ and his disciples, Thomas reveals that Christ did not mean the peace of the world, but rather a greater peace. Certainly, he did not mean peace between barons, bishops, and kings in the country of England not yet invented, and considering that the disciples lived lives of misery in service of Christ, it is unlikely Christ meant peace in the sense of worldly comfort free of strife.
Thomas reminds the congregation that the day after Christmas is a day of celebration for Christ's "first martyr, the blessed Stephen." Thomas does not believe this proximity is an accident – rather, he believes that the mystery of Christmas is paralleled on a smaller scale in the celebration of martyrs, since we engage in the contradiction of celebrating death for them. For martyrs, "we mourn, for the sins of the world that has martyred them; we rejoice, that another soul is numbered among the Saints in Heaven, for the glory of God and for the salvation of men" (199).
Thomas then analyzes the concept of martyrdom, insisting that a martyr is not merely one who dies for Christ, since these things can happen by accident and "Saints are not made by accident" (199). Worldly ambition, which can often lead to martyrdom, has no place in heaven. It is a human creation, and therefore martyrs who die through ambition will not reach the full extent of glorious death. Instead, "the true martyr is he who has become the instrument of God, who has lost his will in the will of God, not lost it but found it, for he has found freedom in his submission to God" (199). It is a profound and mysterious concept, Thomas notes, and accounts for the mystery of its celebration.
Thomas closes his sermon by sharing, "I do not think I shall ever preach to you again" (200). He alludes to the potential of his impending death and martyrdom and begs the congregation to remember his words.
The Interlude, one of the only two prose sections in the play, is a fascinating interjection into the drama for several reasons. It sums up the play's basic philosophy/theology, reveals how fully Thomas has been altered in Act I, and connects the play to the rituals of both tragedy and the mass.
The sermon explicitly spells out the play's theology. In no uncertain terms, Thomas explains that a true martyr is one who dies without ambition. Coming so soon after the episode with the Fourth Tempter, this reminds the audience of his response that closed Part I. He restates with the clarity of prose that a true martyr is one who has vanquished his 'self' - his personality, ambition, and will - and has accepted that he is God's instrument. He basically preaches the philosophy of active patience as described in the Analysis to Part I, although he does not use the words "action" or "suffering" here.
Becket posits himself as parallel to Christ by suggesting that Christians ought to celebrate martyrdom in the same way (albeit on a lower scale) as they celebrate Christ's sacrifice by death. This enforces the holiness of martyrdom. What both deaths have in common is a sense of opposites, an important theme in the play that is manifest both in the story and in the language of the Chorus in Part II. Holy events contain opposites – in this case, the death of a martyr and the death of Christ are simultaneously worthy of mourning and joy. That a human cannot fully comprehend this mysterious contradiction matters little, as long as the human accepts the contradiction as a fact.
Dramatically, the sermon has little impact. It does reveal to the audience that Thomas has firmly accepted his place as God's instrument; he has vanquished his ambition and is ready to die for the right reason. However, nothing has happened since his final speech of Part I to make us think that he might have changed his mind. The character undergoes no transformation here and does not add much to the ideas presented in Part I. Perhaps Eliot wanted to make certain his audience understood his themes, and perhaps he wanted to announce that Thomas's crisis of faith would not extend into Part II. But this raises an interesting question when reading or viewing the play for the first time: if our protagonist has already reached the apex of his personal journey, where else is there for him to go? How can the play only be half over if there is nowhere left to journey? Compounded with the fact that the audience knows how it will end (Thomas will be murdered in the cathedral), Eliot poses an interesting dramatic challenge he will have to address in Part II.
It's worth considering the theatrical effect of this sermon for Eliot's intended audience. In the expansive Canterbury cathedral, the actor playing Thomas would have taken the pulpit and then preached, the only figure on stage, and with very little indication that this was part of a play rather than an actual sermon. Listening to a sermon drawn somewhat from the historical record of Thomas's final sermon on Christmas Day, 1170 must have been a rich, profound theatrical experience, complicating the lines of fiction, myth, and reality for audience members.
This effect is in line with Eliot's intent to structure the experience of his play alongside that of a mass. Again, he is interested more in ritual than storytelling, and both the theatricality and the substance of this sermon reinforce that intention. In terms of theatricality, his play has explicitly become a mass. In terms of substance, Thomas preaches about the mystery and contradiction of celebrating and mourning at the same time. This is an experience that transcends intellectualism. It is about visceral connection and faith, a community whose shared passions are made manifest through a ritual. By putting these ideas into the play, Eliot sets himself up to make Thomas's murder in Act II not a climax (again, the protagonist in many ways reaches his climax in Part I, and will not falter from his resolve), but rather a ritual.
Some of the ideas in the sermon also echo those of Greek tragedy. At its core, Greek tragedy embodies a similar contradiction as that of saint celebration. It looks mournfully and honestly on the unfortunate forces of the world that destroyed individuals, while simultaneously celebrating those individuals who stayed strong in the face in those forces. In many ways, this is the message of the sermon. We celebrate those individuals who were strong enough to die for God and vanquish their personalities for God, but we also mourn that the iniquity of the world required their death. What Eliot's play has that Greek tragedy lacks is the lynchpin of faith. Greeks did not celebrate in the promise of afterlife in their tragedies, while the Christians for whom Eliot writes celebrate someone like Becket not only for his strength, but because he reminds them that they will be rewarded for their own strength in heaven.