The seafarer advocates finding friendship rather than riches.
In the poem, seafaring is a metaphor for the journey of life. As he describes his difficult journey, the speaker notes that friends are the real treasure.
And though he strew the grave with gold,
His born brothers, their buried bodies
Be an unlikely treasure hoard.
This message is repeated several times, and he builds to it in the poem.
Days little durable,
And all arrogance of earthen riches,
There come now no kings nor Cæsars
Nor gold-giving lords like those gone.
The point is that life is a journey. Some people go through this journey collecting riches. Yet most of us also collect friends. The friends are the real riches. They are the valuable ones. When we are at the end of our journey, they are all that matters.
Live life to the fullest. Enjoy it while you can. But be sure to acknowledge where the real wealth is. It lies not in riches, but in who we are and who we love.