Augustine of Hippo — as excerpted in the Catena Aurea on John 14:1-4

“(Tract. lxviii. 1) But why does He go and prepare a place, if there are many mansions already? Because these are not as yet so prepared as they will be. The same mansions that He hath prepared by predestination, He prepares by operation. They are prepared already in respect of predestination; if they were not, He would have said, I will go and prepare, i. e. predestinate, a place for you; but inasmuch as they are not yet prepared in respect of operation, He says, And if I go and prepare a place for you. And now He is preparing mansions, by preparing occupants for them. Indeed, when He says, In My Father’s house are many mansions, what think we the house of God to be but the temple of God, of which the Apostle saith, The temple of God is holy, which temple ye are. (1 Cor. 3:17) This house of God then is now being built, now being prepared. (c. 3.). But why has He gone away to prepare it, if it is ourselves that He prepares: if He leaves us, how can He prepare us? The meaning is, that, in order that those mansions may be prepared, the just must live by faith: and if thou seest, there is no faith. Let Him go away then, that He be not seen; let Him be hid, that He be believed. Then a place is prepared, if thou live by faith: let faith desire, that desire may enjoy. If thou rightly understandest Him, He never leaves either the place He came from, or that He goes from. He goes, when He withdraws from sight, He comes, when He appears. But except He remain in power, that we may grow in goodness, no place of happiness will be prepared for us.”