The speaker describes the word in his time as rough, and imagines that things were wonderful before.
The Sea-farer is drawn to the sea, even though it’s a rough life. He makes many comparisons, and one comparison he makes is between life in his time and the olden days “when the kingdoms of earth flourished in glory.”
Now there are no rulers, no emperors,
No givers of gold, as once there were,
When wonderful things were worked among them
And they lived in lordly magnificence.
Things were great before, but now there is not much other than suffering.
The speaker comments that “the weakest survives and the world continues” because it is “kept spinning by toil.” This reinforces the speaker’s descriptions of his difficult life at sea and how he is drawn back to it.
See the text here: http://www.enotes.com/seafarer/text-poem
See a "translated" text here: http://www.poetryintranslation.com/PITBR/English/Seafarer.htm