St. Ambrose states that after the explanations he has already given of holy living, he will now explain the Mysteries. Then after giving his reasons for not having done so before, he explains the mystery of the opening of the ears, and shows how this was of old done by Christ Himself.
1. We have spoken daily upon subjects connected with morals, when the deeds of the Patriarchs or the precepts of the Proverbs were being read, in order that being taught and instructed by these you might grow accustomed to enter the ways of the ancients and to walk in their paths, and obey the divine commands; in order that being renewed by baptism you might hold to that manner of life which beseems those who are washed.
2. The season now warns us to speak of the Mysteries, and to set forth the purport of the sacraments, which if we had thought it well to teach before baptism to those who were not yet initiated, we should be considered rather to have betrayed than to have portrayed the Mysteries. And then, too, another reason is that the light itself of the Mysteries will shed itself with more effect upon those who are expecting they know not what, than if any discourse had come beforehand.
3. Open, then, your ears, inhale the good savour of eternal life which has been breathed upon you by the grace of the sacraments; which was signified to you by us, when, celebrating the mystery of the opening, we said, “Epphatha, which is, Be opened,” that whosoever was coming in quest of peace might know what he was asked, and be bound to remember what he answered.
4. Christ made use of this mystery in the Gospel, as we read, when He healed him who was deaf and dumb. But He touched the mouth, because he who was healed was dumb and was a man, as regards one point that he might open his mouth with the sound of the voice given to him; as regards the other point because that touch was seemly towards a man, but would have been unseemly towards a woman.
Source: On the Mysteries (New Advent)