1 Therefore Abraham also, knowing the Father through the Word, who made heaven and earth, confessed Him to be God; and having learned, by an announcement [made to him], that the Son of God would be a man among men, by whose advent his seed should be as the stars of heaven, he desired to see that day, so that he might himself also embrace Christ; and, seeing it through the spirit of prophecy, he rejoiced. Wherefore Simeon also, one of his descendants, carried fully out the rejoicing of the patriarch, and said: “Lord, now let Your servant depart in peace. For my eyes have seen Your salvation, which You have prepared before the face of all people: a light for the revelation of the Gentiles, and the glory of the people Israel.” And the angels, in like manner, announced tidings of great joy to the shepherds who were keeping watch by night. Moreover, Mary said, “My soul does magnify the Lord, and my spirit has rejoiced in God my salvation;” — the rejoicing of Abraham descending upon those who sprang from him—those, namely, who were watching, and who beheld Christ, and believed in Him; while, on the other hand, there was a reciprocal rejoicing which passed backwards from the children to Abraham, who did also desire to see the day of Christ's coming. Rightly, then, did our Lord bear witness to him, saying, “Your father Abraham rejoiced to see my day; and he saw it, and was glad.”
2. For not alone upon Abraham's account did He say these things, but also that He might point out how all who have known God from the beginning, and have foretold the advent of Christ, have received the revelation from the Son Himself; who also in the last times was made visible and passible, and spoke with the human race, that He might from the stones raise up children unto Abraham, and fulfil the promise which God had given him, and that He might make his seed as the stars of heaven, as John the Baptist says: “For God is able from these stones to raise up children unto Abraham.” Now, this Jesus did by drawing us off from the religion of stones, and bringing us over from hard and fruitless cogitations, and establishing in us a faith like to Abraham. As Paul does also testify, saying that we are children of Abraham because of the similarity of our faith, and the promise of inheritance.
3. He is therefore one and the same God, who called Abraham and gave him the promise. But He is the Creator, who does also through Christ prepare lights in the world, [namely] those who believe from among the Gentiles. And He says, “You are the light of the world;” that is, as the stars of heaven. Him, therefore, I have rightly shown to be known by no man, unless by the Son, and to whomsoever the Son shall reveal Him. But the Son reveals the Father to all to whom He wills that He should be known; and neither without the goodwill of the Father nor without the agency of the Son, can any man know God. Wherefore did the Lord say to His disciples, “I am the way, the truth, and the life and no man comes unto the Father but by Me. If you had known Me, you would have known My Father also: and from henceforth you have both known Him, and have seen Him.” From these words it is evident, that He is known by the Son, that is, by the Word.
4. Therefore have the Jews departed from God, in not receiving His Word, but imagining that they could know the Father [apart] by Himself, without the Word, that is, without the Son; they being ignorant of that God who spoke in human shape to Abraham, and again to Moses, saying, “I have surely seen the affliction of My people in Egypt, and I have come down to deliver them.” For the Son, who is the Word of God, arranged these things beforehand from the beginning, the Father being in no want of angels, in order that He might call the creation into being, and form man, for whom also the creation was made; nor, again, standing in need of any instrumentality for the framing of created things, or for the ordering of those things which had reference to man; while, [at the same time,] He has a vast and unspeakable number of servants. For His offspring and His similitude do minister to Him in every respect; that is, the Son and the Holy Spirit, the Word and Wisdom; whom all the angels serve, and to whom they are subject. Vain, therefore, are those who, because of that declaration, “No man knows the Father, but the Son,” do introduce another unknown Father.
Source: Adversus haereses (New Advent)