The poem, written in an ABAB pattern, is meant to inspire its readers to live actively, and neither to lament the past nor to take the future for granted. The didactic message is underscored by a vigorous trochaic meter and frequent exclamation. Answering a reader's question about the poem in 1879, Longfellow himself summarized that the poem was "a transcript of my thoughts and feelings at the time I wrote, and of the conviction therein expressed, that Life is something more than an idle dream." Richard Henry Stoddard referred to the theme of the poem as a "lesson of endurance".
Longfellow wrote "A Psalm of Life" at the beginning of a period in which he showed an interest in the Judaic, particularly strong in the 1840s and 1850s. More specifically, Longfellow looked at the American versions or American responses to Jewish stories. Most notable in this strain is the poet's "The Jewish Cemetery at Newport", inspired by the Touro Cemetery in Newport, Rhode Island.
Further, the influence of Goethe was noticeable. In 1854, an English acquaintance suggested "A Psalm of Life" was merely a translation. Longfellow denied this, but admitted he may have had some inspiration from him as he was writing "at the beginning of my life poetical, when a thousand songs were ringing in my ears; and doubtless many echoes and suggestions will be found in them. Let the fact go for what it is worth".