Your father Abraham rejoiced to see my day: and he saw it, and was glad. Abraham rejoiced to see my day - Or, he earnestly desired to see my day; ηγαλλιασατο, from αγαν, very much, and ἁλλομαι, I leap - his soul leaped forward in earnest hope and strong expectation that he might see the incarnation of Jesus Christ. The metaphor appears to be taken from a person who, desiring to see a long-expected friend who is coming, runs forward, now and then jumping up to see if he can discover him. There is a saying very like this in Sohar Numer fol. 61: "Abraham rejoiced because he could know, and perceive, and cleave to the Divine Name." The Divine name is יהוה Yehovah; and by this they simply mean God himself.
And he saw it - Not only in the first promise, Genesis 3:15, for the other patriarchs saw this as well as he; and not only in that promise which was made particularly to himself, Genesis 12:7; Genesis 22:18, (compared with Galatians 3:16), that the Messiah should spring from his family; but he saw this day especially when Jehovah appeared to him in a human form, Genesis 18:2, Genesis 18:17, which many suppose to have been a manifestation of the Lord Jesus.