8 He instances, in proof of this, the case of infants who have just been born, the cry of whom, as soon as they have issued from the womb, is in accordance with the sound of every one of these elements. As, then, he says, the seven powers glorify the Word, so also does the complaining soul of infants. For this reason, too, David said: “Out of the mouth of babes and sucklings You have perfected praise;” and again: “The heavens declare the glory of God.” Hence also it comes to pass, that when the soul is involved in difficulties and distresses, for its own relief it calls out, “Oh” (Ω), in honour of the letter in question, so that its cognate soul above may recognise [its distress], and send down to it relief.
Source: Adversus haereses (New Advent)