Charles Ellicott Commentary Genesis 18:2

"and he lifted up his eyes and looked, and, lo, three men stood over against him: and when he saw them, he ran to meet them from the tent door, and bowed himself to the earth," — Genesis 18:2 (ASV)

Three men. —Jewish commentators explain the number by saying that, as no angel might execute more than one commission at a time, one of the three came to heal Abraham, the second to bear the message to Sarah, and the third to destroy Sodom.

More correctly, one was “the angel of Jehovah,” who came as the manifestation of Deity to Abraham, and the other two were his companions, commissioned by him afterwards to execute judgment on the cities of the plain.

The number three also pointed to the Trinity of Persons in the Godhead and is therefore read by our Church as one of the lessons for Trinity Sunday. But we must be careful not to use it as a proof of this doctrine, lest the inference be drawn of a personal appearance of the Father and of the Holy Spirit, which would savour of heretical impiety.