But if the mental voice of those who pray should not be extremely loud, though it is not weak, and should they not raise a cry and shout, God still hears those who pray thus. For it is he who says to Moses, “Why do you cry out to me?” when he had not cried out audibly (for this is not recorded in Exodus), but through prayer he had cried out loudly in that voice which is heard by God alone.
Or do you not hear how Moses, although he said nothing but met the Lord with his inexpressible groanings, was heard by the Lord, who said, “Why do you cry to me?” God knows how to hear even the blood of a just man, to which no tongue is attached and of which no voice pierces the air. The presence of good works is a loud voice before God.
The word cry in Scripture does not refer to the cry of the voice but to the cry of the heart. In fact, the Lord says to Moses, “Why are you crying out to me?” when Moses had not muttered any cry at all.
The heart reveals its silent longing, to which the Godhead listens more than to the most thundering voices of nations. He said to Moses, “Why do you cry to me?” although we do not read that Moses had said anything. So the faithful man said that his heart was speaking to the Lord, since he seemed to offer his thoughts by this means.
[AD 253] Origen of Alexandria on Exodus 14:15