This is a title of respect. Possible meanings are 1) Abraham knew that one of these men was God or 2) Abraham knew that these men came on behalf of God.
Here "found favor" is an idiom that means be approved of or that the Lord is pleased with him, and "your sight" is a metaphor representing the Lord's evaluation. Alternate translation: "if you have evaluated me and approve" or "if you are pleased with me" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-metaphor]])