When love has cast out fear from our souls completely, and all fear in us has been transformed into love, then the unity which is the gift of our Saviour will be fully realized among us, because we will all be united with each other through our union with the one supreme Good. Following his ascension, after conferring all power on his disciples by his blessing, our Lord obtained many other gifts for them by his prayer to the Father. Among these was the greatest gift of all, which was that they were no longer to be divided in their judgement about what was right and good, because they were all to be united to the one supreme Good. As the Apostle says, they were to be bound together with the bonds of peace in the unity that comes from the Holy Spirit. They were to be made one body and one spirit by the one hope to which they were all called.
We shall do well, however, to quote the sacred words of the gospel itself. ‘I pray, the Lord says. ‘that they all may be one; that as you, Father, are in me and I am in you, so they also may be one in us.’ Now the bond that creates this unity is glory. That the Holy Spirit is called glory no one can deny if one reflects upon our Lord’s words: ‘The glory you gave to me, I have given to them.’ In fact, he gave this glory to his disciples when he said to them: ‘Receive the Holy Spirit.’ Although he had always possessed it, even before the world existed, our Lord received this glory when he put on human nature. Then, when his human nature had been glorified by the Spirit, the glory of the Spirit was passed on to all his brothers and sisters, beginning with his disciples. This is why he said: ‘The glory you gave to me, I have given to them, so that they may be one as we are one. With me in them and you in me, I want them to be perfectly one. Whoever then grows from infancy to adulthood and attains to spiritual maturity possesses the mastery of human compulsions and an inner purity that makes it possible to receive the glory of the Spirit.
— From a homily of Gregory of Nyssa (330-395)