4 But when He says, “I will ask the Father, and He shall give you another Paraclete,” He intimates that He Himself is also a paraclete. For paraclete is in Latin called advocatus (advocate); and it is said of Christ, “We have an advocate with the Father, Jesus Christ the righteous.” But He said that the world could not receive the Holy Spirit, in much the same sense as it is also said, “The minding of the flesh is enmity against God: for it is not subject to the law of God; neither indeed can be;” just as if we were to say, Unrighteousness cannot be righteous. For in speaking in this passage of the world, He refers to those who love the world; and such a love is not of the Father. And thus the love of this world, which gives us enough to do to weaken and destroy its power within us, is in direct opposition to the love of God, which is shed abroad in our hearts by the Holy Spirit who is given unto us. “The world,” therefore, “cannot receive Him, cause it sees Him not, neither knows Him.” For worldly love possesses not those invisible eyes, whereby, save in an invisible way, the Holy Spirit cannot be seen.
5. “But you,” He adds, “shall know Him; for He shall dwell with you, and be in you.” He will be in them, that He may dwell with them; He will not dwell with them to the end that He may be in them: for the being anywhere is prior to the dwelling there. But to prevent us from imagining that His words, “He shall dwell with you,” were spoken in the same sense as that in which a guest usually dwells with a man in a visible way, He explained what “He shall dwell with you” meant, when He added the words, “He shall be in you.” He is seen, therefore, in an invisible way: nor can we have any knowledge of Him unless He be in us. For it is in a similar way that we come to see our conscience within us: for we see the face of another, but we cannot see our own; but it is our own conscience we see, not another's. And yet conscience is never anywhere but within us: but the Holy Spirit can be also apart from us, since He is given that He may also be in us. But we cannot see and know Him in the only way in which He may be seen and known, unless He be in us.
Source: Tractates on the Gospel of John (New Advent)