What does Emerson mean in his poem Give All to Love?

I think the speaker is saying to love without restraint the one your with, and the transcendental part is in the little note that pops up at the poem's end on your link. It basically says that when something ends, as when someone leaves, as the poem says that will happen, whether from death or the person finds someone new, welcome it as a change that the life is configuring to allow you and the person leaving to grow and evolve. The last two lines about half gods leaving and full ones coming is I think saying that your life is being lived half-way and is being terminated for a fuller life to come in.