A question, how it is that in the Apostle's chapter, after he has spoken of the lusts of the flesh and spirit opposing one another, he adds a third thing; viz., man's will.
Germanus: Although some glimmer of the sense now seems clear to us, yet as we cannot thoroughly grasp the Apostle's meaning, we want you to explain this more clearly to us. For the existence of three things seems to be indicated here: first, the struggle of the flesh against the spirit, secondly the desire of the spirit against the flesh, and thirdly our own free will, which seems to be placed between the two, and of which it is said: “You should not do what you will.” And on this subject though as I said we can gather some hints, from what you have explained of the meaning, yet— since this conference gives the opportunity— we are anxious to have it more fully explained to us.
Source: Conferences (New Advent)