Quotes about Abraham and the banquet:
Severian of Gabbala: "Christ appeared to you, O excellent one, escorted by two angels, and by your hospitality you became a companion of God and of angels… Christ appeared to you in the appearance of a man, revealing to you the mysteries of his divine and saving sojourn on earth… Therefore you recognised God's mediator, the Son who was to be known between two living beings or animals."
Justin Martyr: "Moses, therefore, that blessed and faithful servant of God, declares that the one who was seen by Abraham at the oak of Mamre was God, accompanied by two angels, who were sent, for the condemnation of Sodom, by another, namely by the One who always remains above the heavens, who has never been seen by any human being, and who of himself holds converse with none, whom we term the Creator of all things, and the Father."
St. Ambrosius: "The Lord Christ is probably coming in the person of the stranger or the poor, having said: "I was in prison and you came to Me; I was naked and you clothed Me" (Matthew 25: 36)."
St. Jerome: "The true temple for Christ is the believer’s soul; So let us adorn it; :Let us offer Him clothes, and gifts; Let us welcome Christ in him ! What would be the use of walls adorned with jewels, if Christ in the poor, is in danger of death because of hunger ?."
Moses and the bush:
Justin Martyr: "Neither Abraham, nor Isaac, nor Jacob, nor any other man, ever saw the Father and Ineffable Lord of all things…; but the One who according to his will is both God his Son and his Angel ministering to his will, whom he determined should be born as man of a Virgin, and who once even became fire when he conversed with Moses from the bush."
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Patristic teaching holds that ‘the Angel of the Lord’ is one of the many names of God the Word in the Old Testament. It is, in fact, one of the earliest Christological titles. More often than not, ‘the Angel of the Lord’ refers not to one of the bodiless powers of heaven, but to the pre-incarnate Christ. Angel means messenger, and in the Old Testament an “angel” was not necessarily one of the heavenly court – it could also be a human being. The Word is God’s messenger par excellence. Thus St Justin Martyr repeatedly refers to Christ as an Angel. The primary source for Justin and other Church Fathers was probably the Septuagint translation of Isaiah 9:6:
“For a child is born to us, and a son is given to us, whose government is upon his shoulder: and his name is called the Angel of Great Counsel: for I will bring peace upon the princes, and health to him”.
And yet Justin, despite his copious use of the term ‘Angel of the Lord’ or ‘Angel of Great Counsel’, never attempts to clarify that the Angel is the Word of God, for that Christ was called Angel was obvious to anyone who was familiar with the Septuagint Isaiah 9:6. Since it was widely acknowledged that Isaiah 9:6 refers to the Messiah, the title “Angel of Great Counsel” refers also to Christ, and thus it also follows that Christ is the Angel of the Lord who appears to the Prophets of the Old Testament (e.g. Genesis 15–22; Genesis 28–35; Exodus 3, Joshua 5-6).
Justin argued from the appearances of the Angel in the Old Testament that this Angel is God Himself. This is explained by Günther Juncker in his treatment of the subject:
‘It does not take Justin long to point out from the Old Testament appearances of the Angel of the Lord that this Angel is fully God. Invariably when this particular Angel is seen, those who have seen him declare that they have seen God and are amazed that they have lived. In numerous places this Angel speaks in the first person as Lord and God, receives worship and sacrifices, and makes the very ground on which he stands holy; yet in other places he speaks of God in the third person and is functionally subordinate since, as Angel, he is sent by God to deliver a message from God. When these passages were combined with others (e.g. Gen 1:26; 24 19:24; Ps 45:6–7; and 110:1) which on the surface seem to speak of a plurality of persons in the Godhead, Justin’s argument became irrefutable. Thus in a key passage which mentions the title Angel four times in relation to the Old Testament theophanies, Justin can hardly be held guilty of an overstatement when he says of Christ that “He is called God, He is God, and shall always be God” (Dial. 58)’
[“Christ As Angel: The Reclamation Of A Primitive Title,” Trinity Journal 15:2 (Fall 1994): 221–250.]
In his Dialogue with Trypho, Justin writes:
‘He who is called God and appeared to the patriarchs is called both Angel and Lord, in order that from this you may understand Him to be minister to the Father of all things... He… appeared as a man to Abraham, and… wrestled in human form with Jacob’
Sources:
http://www.pravmir.com/article_1224.html and Father Tadros Malaty