"The Seafarer" is an anonymous Old English poem that survives in the tenth century Exeter Book, a collection of Old English poetry donated to Exeter Cathedral. Although the poem probably existed in one or more oral versions before it was first captured in writing, and the current form of the poem may differ from other version that are no longer extant, there is no compelling reason to consider the Christian elements as something separate or added on to the poem, nor would the original performers or audiences have considered them a window to religious history.
One essential characteristic of oral culture is what is known as homeostasis, the way stories and songs about the past are currently updated in light of current practices. Rather than history being something fixed and academic, it was regarded as a resource for understanding how one should behave in the present, and historical accounts updated as circumstances changed. Rather than thinking of the Christian principles as an overlay, the original readers would have understood them as the most profound part of the poem, proving the greater divine context for the human world of seafaring, and fitting the local and ephemeral into a broader system of universal revealed truth. Instead, the poem acts as a performable and memorable narrativization of behavioral norms, both in seafaring and general moral and religious conduct.