These are the feet that David washes in spirit when he teaches you how to keep them unsoiled, saying, "Our feet have been standing in your courts, O Jerusalem." Certainly, here "feet" is to be understood not as of the body but as of the soul. For how could a person on earth have his physical feet in heaven? Since Jerusalem, as Paul tells you, is in heaven, he also shows you how to stand in heaven when he says, "But our abode is in heaven": 2 the "abode" of your behavior, the "abode" of your deeds, the "abode" of your faith.
Source: Concerning Virginity 9:59