18 Thus, the teacher of humility came not to do His own will, but the will of Him that sent Him. Let us come to Him, enter in unto Him, be ingrafted into Him, that we may not be doing our own will, but the will of God: and He will not cast us out, because we are His members, because He willed to be our head by teaching us humility. Finally, hear Himself discoursing: “Come unto me, you who labor and are heavy laden: take my yoke upon you, and learn of me; for I am meek and lowly of heart:” and when you have learned this, “you shall find rest for your souls,” from which you cannot be cast out; “because I have come down from heaven, not to do my own will, but the will of Him that sent me;” I teach humility; none but the humble can come unto me. Only pride casts out; how can he go out who keeps humility and falls not away from the truth? So much as could be said about the hidden sense has now been said, brethren: this sense is hidden enough, and I know not whether I have drawn out and shaped in suitable words for you, why it is that He casts not out him that comes unto Him; because He came not to do His own will, but the will of Him that sent Him.
Source: Tractates on the Gospel of John (New Advent)