How do both pagan and Christian ideas coexist in The Seafarer?

In "The Seafarer," the speaker talks about the realities of life as a seafarer on the ocean and the excitement, danger, beauty, and suffering that accompanies such a life. Within this description of life, the speaker often references God and Fate and their roles in his earthly voyage. The speaker encourages one to put their trust in God and to believe that earthly joys and pain pale in comparison to seeking a heavenly afterlife.
However, the speaker also talks about Fate in a pagan context, referencing Fate as a more chaotic force that exists throughout the universe and that can not be fought against. However, the speaker uses the idea of Fate to emphasize that humans can not simply resist the suffering and random trials of the universe without relying on God.