For having heard in Egypt that God had said to Moses, when He was about to send him to the Hebrews, “I am that I am,” he understood that God had not mentioned to him His own proper name.
For God cannot be called by any proper name, for names are given to mark out and distinguish their subject-matters, because these are many and diverse; but neither did any one exist before God who could give Him a name, nor did He Himself think it right to name Himself, seeing that He is one and unique, as He Himself also by His own prophets testifies, when He says, “I God am the first,” and after this, “And beside me there is no other God.” On this account, then, as I before said, God did not, when He sent Moses to the Hebrews, mention any name, but by a participle He mystically teaches them that He is the one and only God. “For,” says He; “I am the Being;” manifestly contrasting Himself, “the Being,” with those who are not, that those who had hitherto been deceived might see that they were attaching themselves, not to beings, but to those who had no being.
Justin Martyr
Hortatory Address to the Greeks
Chapter XX & XXI