The God of the Law and the Prophets, and the Father of Our Lord Jesus Christ, is the Same God
1 Having now briefly arranged these points in order as we best could, it follows that, agreeably to our intention from the first, we refute those who think that the Father of our Lord Jesus Christ is a different God from Him who gave the answers of the law to Moses, or commissioned the prophets, who is the God of our fathers, Abraham, Isaac, and Jacob. For in this article of faith, first of all, we must be firmly grounded. We have to consider, then, the expression of frequent recurrence in the Gospels, and subjoined to all the acts of our Lord and Saviour, “that it might be fulfilled which was spoken by this or that prophet,” it being manifest that the prophets are the prophets of that God who made the world. From this therefore we draw the conclusion, that He who sent the prophets, Himself predicted what was to be foretold of Christ. And there is no doubt that the Father Himself, and not another different from Him, uttered these predictions. The practice, moreover, of the Saviour or His apostles, frequently quoting illustrations from the Old Testament, shows that they attribute authority to the ancients. The injunction also of the Saviour, when exhorting His disciples to the exercise of kindness, “Be perfect, even as your Father who is in heaven is perfect; for He commands His sun to rise upon the evil and the good, and sends rain on the just and on the unjust,” most evidently suggests even to a person of feeble understanding, that He is proposing to the imitation of His disciples no other God than the maker of heaven and the bestower of the rain. Again, what else does the expression, which ought to be used by those who pray, “Our Father who art in heaven,” appear to indicate, save that God is to be sought in the better parts of the world, i.e., of His creation? Further, do not those admirable principles which He lays down respecting oaths, saying that we ought not to “swear either by heaven, because it is the throne of God; nor by the earth, because it is His footstool,” harmonize most clearly with the words of the prophet, “Heaven is My throne, and the earth is My footstool?” And also when casting out of the temple those who sold sheep, and oxen, and doves, and pouring out the tables of the money-changers, and saying, “Take these things, hence, and do not make My Father's house a house of merchandise,” He undoubtedly called Him His Father, to whose name Solomon had raised a magnificent temple. The words, moreover, “Have you not read what was spoken by God to Moses: I am the God of Abraham, and the God of Isaac, and the God of Jacob; He is not a God of the dead, but of the living,” most clearly teach us, that He called the God of the patriarchs (because they were holy, and were alive) the God of the living, the same, viz., who had said in the prophets, “I am God, and besides Me there is no God.” For if the Saviour, knowing that He who is written in the law is the God of Abraham, and that it is the same who says, I am God, and besides Me there is no God, acknowledges that very one to be His Father who is ignorant of the existence of any other God above Himself, as the heretics suppose, He absurdly declares Him to be His Father who does not know of a greater God. But if it is not from ignorance, but from deceit, that He says there is no other God than Himself, then it is a much greater absurdity to confess that His Father is guilty of falsehood. From all which this conclusion is arrived at, that He knows of no other Father than God, the Founder and Creator of all things.
2. It would be tedious to collect out of all the passages in the Gospels the proofs by which the God of the law and of the Gospels is shown to be one and the same. Let us touch briefly upon the Acts of the Apostles, where Stephen and the other apostles address their prayers to that God who made heaven and earth, and who spoke by the mouth of His holy prophets, calling Him the “God of Abraham, of Isaac, and of Jacob;” the God who “brought forth His people out of the land of Egypt.” Which expressions undoubtedly clearly direct our understandings to faith in the Creator, and implant an affection for Him in those who have learned piously and faithfully thus to think of Him; according to the words of the Saviour Himself, who, when He was asked which was the greatest commandment in the law, replied, “You shall love the Lord your God with all your heart, and with all your soul, and with all your mind. And the second is like it, You shall love your neighbour as yourself.” And to these He added: “On these two commandments hang all the law and the prophets.” How is it, then, that He commends to him whom He was instructing, and was leading to enter on the office of a disciple, this commandment above all others, by which undoubtedly love was to be kindled in him towards the God of that law, inasmuch as such had been declared by the law in these very words? But let it be granted, notwithstanding all these most evident proofs, that it is of some other unknown God that the Saviour says, “You shall love the Lord your God with all your heart,” etc., etc. How, in that case, if the law and the prophets are, as they say, from the Creator, i.e., from another God than He whom He calls good, shall that appear to be logically said which He subjoins, viz., that “on these two commandments hang the law and the prophets?” For how shall that which is strange and foreign to God depend upon Him? And when Paul says, “I thank my God, whom I serve in my spirit from my forefathers with pure conscience,” he clearly shows that he came not to some new God, but to Christ. For what other forefathers of Paul can be intended, except those of whom he says, “Are they Hebrews? So am I: are they Israelites? So am I.” Nay, will not the very preface of his Epistle to the Romans clearly show the same thing to those who know how to understand the letters of Paul, viz., what God he preaches? For his words are: “Paul, the servant of Jesus Christ, called to be an apostle, set apart to the Gospel of God, which He had promised afore by His prophets in the holy Scriptures concerning His Son, who was made of the seed of David according to the flesh, and who was declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead of Christ Jesus our Lord,” etc. Moreover, also the following, “You shall not muzzle the mouth of the ox that treads out the grain. Does God take care for oxen? Or says he it altogether for our sakes? For our sakes, no doubt, this is written, that he that ploughs should plough in hope, and he that threshes in hope of partaking of the fruits.” By which he manifestly shows that God, who gave the law on our account, i.e., on account of the apostles, says, “You shall not muzzle the mouth of the ox that treads out the grain;” whose care was not for oxen, but for the apostles, who were preaching the Gospel of Christ. In other passages also, Paul, embracing the promises of the law, says, “Honour your father and your mother, which is the first commandment with promise; that it may be well with you, and that your days may be long upon the land, the good land, which the Lord your God will give you.” By which he undoubtedly makes known that the law, and the God of the law, and His promises, are pleasing to him.
Source: De Principiis (New Advent)