51 In all truth I tell you, whoever keeps my word will never see death.
52 The Jews said, `Now we know that you are possessed. Abraham is dead, and the prophets are dead, and yet you say, "Whoever keeps my word will never know the taste of death."
53 Are you greater than our father Abraham, who is dead? The prophets are dead too. Who are you claiming to be?`
54 Jesus answered: If I were to seek my own glory my glory would be worth nothing; in fact, my glory is conferred by the Father, by the one of whom you say, `He is our God,`
55 although you do not know him. But I know him, and if I were to say, `I do not know him,` I should be a liar, as you yourselves are. But I do know him, and I keep his word.
56 Your father Abraham rejoiced to think that he would see my Day; he saw it and was glad.
57 The Jews then said, `You are not fifty yet, and you have seen Abraham!`
58 Jesus replied: In all truth I tell you, before Abraham ever was, I am.
59 At this they picked up stones to throw at him; but Jesus hid himself and left the Temple.
Commentary of the day
Saint Caesarius of Arles (470-543), monk and Bishop
"Abraham saw my day"
Now where did this meeting [between Abraham and his three guests] take place? «By the oak of Mamre», which means «vision» or even «insight». Do you see what kind of place it is where the Lord can arrange a meeting? It is true that Abraham`s qualities of discernment and insight were pleasing to the Lord; he had a heart pure enough to be able to see God (cf. Mt 5,8). In such a place and in such a heart could the Lord assemble his guests.
Our Lord spoke to the Jews about this meeting in the Gospel. He said to them: «Your father, Abraham, rejoiced to see my day. He saw it and was glad». He says, «He saw my day» because Abraham recognised the mystery of the Trinity. In his own time he saw the Father, the Son and the Holy Spirit and all three persons joined together in a single day, just as God the Father, God the Son and God the holy Spirit are all three but a single God. Indeed, each of the divine persons in particular is God in his entirety and, at the same time, all three together are God. So it is not incongruous to discern the Father, Son and Holy Spirit in the three measures of flour Sarah brought since they have a unity of substance.
Nevertheless, we might put forward another interpretation and see in Sarah an image of the Church. The three measures of flour may be interpreted as faith, hope and love. In fact, these three virtues unite the fruits of the universal Church. Everyone who has been worthy of uniting these three virtues in himself may be assured of receiving in his heart the Trinity as a whole.