While the poem begins with descriptions of the sea and descriptions of the narrator's personal sorrow, it starts discussing the Christian idea of an afterlife in line 56. The man describes his soul leaving his body, sorrowing over the sea and searching for Heaven. He concludes that the "joys of the Lord" are better than the "dead life" on Earth. He emphasizes he belief that success in the world will not determine the soul's destiny. Rather, he states that living an honorable life, faithful to God, will lead the soul to eternal joy in Heaven. Here, the author reveals his Christian belief that the faithful will be rewarded in the afterlife.
Many scholars of medieval literature note similarities in style and content between "The Seafarer" and the wisdom literature of the Judeo-Christian scriptures. Like the Old Testament poetry books of Proverbs, Job and Ecclesiastes, "The Seafarer" discusses the impermanence of a man's life on Earth and the pointlessness of wealth, earthly pleasures and striving toward transitory goal. The idea that a man should figuratively "steer" his ship toward God's wisdom is deeply Christian and echoes the sentiments of the patriarchs of the Old Testament.
As the narrator waxes about life as a mariner, he reveals his belief in God as the most faithful Lord. While on land, he wonders, beginning in line 33, whether or not to take again to the sea, stating that there is no earthly lord more faithful, or gracious than God. At this point in the poem, the sea becomes a metaphor for a man' spiritual journey. Just as his ocean voyage is solitary, without community or companionship, so is his voyage toward the afterlife. He must rely entirely on the Lord, the only faithful, stable point in the midst of a tossing sea whose will is sovereign.
In addition to themes about the afterlife, the transitoriness of the Earth and the value of devotion to the Lord, "The Seafarer" holds Christian character virtues in high esteem. Beginning in line 107, the narrator echoes a biblical sentiment from James 4:6 that God gives grace to the humble. He continues to explain that a man must steer his willful heart toward God's will. The narrator advises the reader to cultivate other Christian character qualities including moderation, purity and happiness in both joy and affliction.