I held it truth, with him who sings To one clear harp in divers tones, That men may rise on stepping-stones Of their dead selves to higher things.
But who shall so forecast the years And find in loss a gain to match? Or reach a hand thro' time to catch The far-off interest of tears?
Let Love clasp Grief lest both be drown'd, Let darkness keep her raven gloss: Ah, sweeter to be drunk with loss, To dance with death, to beat the ground,
Than that the victor Hours should scorn The long result of love, and boast, "Behold the man that loved and lost, But all he was is overworn."
Tennyson once believed that men would rise "on stepping stones" (little by little) from death to become something more.
He believed this along with believing in God, whom he presents in the image of someone singing to one harp with many voices. This might strike you as a significant image: music and unity coming from many things or people (remember that reference to music in line 28?).
(FYI: "divers" here means "diverse," not "a group of people who like to dive.")
But now Tennyson is finding it difficult to find a silver lining. His grief is too much.
Plus, people can't transcend time and cut out the grief in between to see what will happen. That would be a nifty trick, though.
Instead, the speaker suggests that we mix love and grief (notice the capital letters—he's personifying these concepts).
It's better, he argues, to be all dark and goth-y and intoxicated with grief than to let time win and gloat that the guy who loved and lost just ended up worn out by it all.
Tennyson is definitely struggling with that old saying, "It's better to have loved and lost than to never have loved at all."