In this selection, St. Cyril is pondering why Christ would say, “It is better for you that I go [away]” (Jn 16:7). “How can this be?” Cyril asks. His answer: because when Christ ascends and begins to reign, he will send the Holy Spirit upon the faithful who will bring to them every blessing from God.
In Cyril’s view, the deep work of God in us is to make us partakers of the divine nature (2 Pt 1:4). This is the true goal of Christ’s saving work. But this can happen only by the Spirit coming to dwell in us. By the Spirit’s action in our lives, we leave behind our old way of life and are internally transformed into a new creation.
Because the Spirit comes to dwell in our hearts — inside of us — he causes “every virtue” to spring up and makes us effective co-workers in his mission. The Spirit gives us “a new disposition” — as Paul says, we become transformed from within and so can live a new Christ-like way of life. This was true for the first disciples and it is still true for us today.
For Cyril, to try to live as a Christian without the presence and power of the Holy Spirit is unthinkable. But with the Spirit who brings us new life and power, we can act boldly as servants of Christ, bringing his mercy and presence to the world.
Cyril of Alexandria, Commentary on John 16:7 
Come, let us consider something else in our contemplation that is also beneficial and true. Everything on earth was finally accomplished, as we just stated. But it was surely also necessary for us to become sharers and participants in the divine nature of the Word, or rather for us to leave our own life and be transformed into another and reshaped into the newness of a God-pleasing way of life. However, it was not possible for us to attain this in any other way than through communion and participation with the Holy Spirit.
The most fitting and appropriate time for the sending of the Spirit and his descent to us was that time in which the due season came: the time after the departure of Christ our Savior. When he was still in the flesh with those who believed in him, he became the supplier, I think, of all blessings. But when the moment and necessity called him to ascend to the Father in heaven, it was essential that he be present through the Spirit to those who worship him and that he dwell in our heart through faith so that, having him in ourselves, we may cry out with boldness, “Abba! Father!” (Gal 4:6) and may readily advance to every virtue and, what is more, may be found strong and invincible against the schemes of the devil as well as human attacks, since we have the almighty Spirit.
It would surely be easy to show, both from the old and the new Scriptures, that the Spirit transfers those in whom he comes and dwells into a new disposition and transforms them into newness of life. The blessed Paul says, “All of us, with unveiled face, seeing the glory of the Lord as though reflected in a mirror, are being transformed into the same image from one degree of glory to another; for this comes from the Lord, the Spirit” (2 Cor 3:18). Do you see how the Spirit transforms those in whom he dwells into another image, as it were? He readily moves them from the desire to set their mind on earthly things to an exclusive contemplation of heavenly things, and from cowardly fear to the most courageous disposition. There is no doubt that we will find that the disciples experienced this and were steeled by the Spirit so that they did not collapse before the assaults of their persecutors but held tight to their love for Christ. Therefore, the Savior’s statement is true when he says, my departure to heaven is “better for you.” That was the proper time for the descent of the Spirit.
 The translation is from Cyril of Alexandria, Commentary on John, vol. 2, Ancient Christian Texts, trans. David R. Maxwell (Downers Grove, IL: IVP Academic, 2015), 252.