6 Do you see, beloved, how many and how great blessings we would have lost, if the Lord had yielded to the exhortation of John, and declined baptism? For the heavens were shut before this; the region above was inaccessible. We would in that case descend to the lower parts, but we would not ascend to the upper. But was it only that the Lord was baptized? He also renewed the old man, and committed to him again the sceptre of adoption. For straightway “the heavens were opened to Him.”
A reconciliation took place of the visible with the invisible; the celestial orders were filled with joy; the diseases of earth were healed; secret things were made known; those at enmity were restored to amity. For you have heard the word of the evangelist, saying, “The heavens were opened to Him,” on account of three wonders. For when Christ the Bridegroom was baptized, it was meet that the bridal-chamber of heaven should open its brilliant gates. And in like manner also, when the Holy Spirit descended in the form of a dove, and the Father's voice spread everywhere, it was meet that “the gates of heaven should be lifted up.” “And, lo, the heavens were opened to Him; and a voice was heard, saying, This is my beloved Son, in whom I am well pleased.”
Source: Discourse on the Holy Theophany (New Advent)