| Quote #4
But just as in the first stanza, the transformation is reversed. Herbert asks to "combine" with God, acknowledging that by himself he's too weak and damaged to turn his life around. At first "combine" seems like a general verb, but it gets a more specific meaning in the last two lines. It's clear that Herbert can't go it alone. He needs to join with God in order to transform himself into something new.
| Quote #5
For, if I imp my wing on thine,
Let's get down in the feathers, folks. Here Herbert gets all nitty-gritty with his bird metaphor, and "imp" gives some precision to the idea of combining with God. Not only does the speaker want healing ("to imp" means to repair); he also wants transformation. He wants to incorporate some of God into himself, to borrow some of God's holy substance (or, in the metaphor, his feathers) to bulk up his soul.