Bede

She called on the name of the Lord who spoke to her: "You are the God who sees me." For she said, "Surely here I have seen the back of the one who sees me," therefore she called that well, "The well of the living one who sees me." It is clear from these words that Hagar could not see the face of the angel speaking with her, but only the back as he was departing; nevertheless, she recognized that she had seen him showing mercy and that he was living, that is, that he was truly God, or had come to her in the presence of the living God. …

Commentary on Genesis (Hexaemeron) ↗