Body and soul, heaven and earth—Donne was obsessed with this central contrast between the life we have to live in this goofy body (I mean, we have to put on deodorant just to keep from smelling funky), yet we feel ourselves endowed with a willful, strong, living spirit. This contrast kept Donne occupied for the better part of his career, as he bounced between poems suitable for the bedroom and poems for his pulpit. In "A Valediction: Forbidding Mourning," Donne contrasts love that is based on the body, with a spiritual love that is able to transcend the flesh and is based on the soul.
Hop on the therapy couch, pal. Donne writes about spiritual love in this way because he is at least partially afraid of his physical body. His more promiscuous early life and writing makes him feel dirty and guilty, and so he praises anything spiritual and speaks poorly about the body.
Of course Donne has to make the argument that spirits matter more than bodies. He is about to be away from his wife's body for months. He's just trying to make himself feel better. (Think it's working?)