Tho' much is taken, much abides; and though We are not now that strength which in old days Moved earth and heaven; that which we are, we are; One equal temper of heroic hearts, Made weak by time and fate, but strong in will To strive, to seek, to find, and not to yield.
Ulysses yet again tells us that even though he and his sailors are old and don't have a lot of gas left in the tank, there's enough left to go a little farther.
"Abides" is a word that means "remains."
These guys are a team with one heartbeat. They're old and broken, but they still have the will to seek out and face challenges without giving up. They can't bench-press 200 pounds anymore, but that won't stop them from trying anyway.
The phrase "strong in will / To strive, to seek, to find, and not yield" means something like "we're strong because of our will to strive" or "our will to strive is strong."