“Why was the Holy Spirit first given to the disciples on earth, and later sent from heaven? Because there are two precepts of love, that is, love of God and of neighbor.
The gift of the Spirit on earth was to bring about love of neighbor, and the gift from heaven was to bring about love of God. Just as there is one love and two precepts, so there is one Spirit and two gifts.
The first gift was made by the Lord when He was abiding on earth and the second from heaven, because in love of our neighbor we learn how we are to arrive at the love of God. Indeed, the same Holy Spirit was present in the hearts of the disciples earlier to give them faith, but was not yet given by a clear bestowal until after the resurrection.
So it is written: ‘The Holy Spirit was not yet given, because Jesus was not yet glorified [Jn. 7:39].’…We must be sure that those who already had the Holy Spirit…received Him openly after the Lord’s resurrection, so that they could be of assistance not just to a few but to many.” [Ib., 202-204.]
Saint Gregory the Great, Orthodox New Testament Volume 1.