Concise Bible Dictionary:

The quotations from the Old Testament in the New are important as proving incontestably that God is the author of the whole. It is not simply that Moses or David said this or that—though the quotations prove that Moses was the writer of the Pentateuch—but they are introduced by such words as “God commanded” (Matt. 15:44For God commanded, saying, Honor thy father and mother: and, He that curseth father or mother, let him die the death. (Matthew 15:4)); “The Holy Ghost saith” (Heb. 3:77Wherefore (as the Holy Ghost saith, To day if ye will hear his voice, (Hebrews 3:7)); “David himself said by the Holy Ghost” (Mark 12:3636For David himself said by the Holy Ghost, The Lord said to my Lord, Sit thou on my right hand, till I make thine enemies thy footstool. (Mark 12:36)); “Spake the Holy Ghost by Esaias the prophet” (Acts 28:2525And when they agreed not among themselves, they departed, after that Paul had spoken one word, Well spake the Holy Ghost by Esaias the prophet unto our fathers, (Acts 28:25)). Then the whole is spoken of as “the scriptures,” which are all inspired by God. Whatever therefore is inscribed with “It is written” has the authority of God Himself.
The quotations from the prophets are introduced in various ways.
1. “In order (ἴνα) that it might be fulfilled” (Matt. 1:2222Now all this was done, that it might be fulfilled which was spoken of the Lord by the prophet, saying, (Matthew 1:22), etc.). The event happens that that prophecy should be fulfilled.
2. “So that (ὅπως) it might be fulfilled” (Matt. 2:2323And he came and dwelt in a city called Nazareth: that it might be fulfilled which was spoken by the prophets, He shall be called a Nazarene. (Matthew 2:23), etc.). Such events fall within the scope of the prophecy, and may also apply at other times.
3. “Then (τότε) was fulfilled” (Matt. 2:1717Then was fulfilled that which was spoken by Jeremy the prophet, saying, (Matthew 2:17), &c). The prophecy applied to that event, without its being the purpose of the prophecy.
The citations also illustrate how the scriptures, both the Old and the New Testaments, may be applied, as when the Lord quoted from Deuteronomy in repelling the temptations of Satan. See also the different applications of Habakkuk 2:44Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith. (Habakkuk 2:4). In Romans 1:1717For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith. (Romans 1:17), it is a question of righteousness: “the just shall live by faith.” In Galatians 3:1111But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith. (Galatians 3:11), it is in contrast to the law: “the just shall live by faith.” And in Hebrews 10:3838Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him. (Hebrews 10:38), it is in contrast to drawing back: “the just shall live by faith.”
The quotations are from Moses, the Psalms, and the Prophets. In those days the books were not divided into chapters and verses as now, which accounts for various expressions. As in Mark 2:2626How he went into the house of God in the days of Abiathar the high priest, and did eat the showbread, which is not lawful to eat but for the priests, and gave also to them which were with him? (Mark 2:26), a quotation is from “[the section] of Abiathar the high priest” (1 Sam. 21:1-61Then came David to Nob to Ahimelech the priest: and Ahimelech was afraid at the meeting of David, and said unto him, Why art thou alone, and no man with thee? 2And David said unto Ahimelech the priest, The king hath commanded me a business, and hath said unto me, Let no man know any thing of the business whereabout I send thee, and what I have commanded thee: and I have appointed my servants to such and such a place. 3Now therefore what is under thine hand? give me five loaves of bread in mine hand, or what there is present. 4And the priest answered David, and said, There is no common bread under mine hand, but there is hallowed bread; if the young men have kept themselves at least from women. 5And David answered the priest, and said unto him, Of a truth women have been kept from us about these three days, since I came out, and the vessels of the young men are holy, and the bread is in a manner common, yea, though it were sanctified this day in the vessel. 6So the priest gave him hallowed bread: for there was no bread there but the showbread, that was taken from before the Lord, to put hot bread in the day when it was taken away. (1 Samuel 21:1‑6)). In Luke 20:3737Now that the dead are raised, even Moses showed at the bush, when he calleth the Lord the God of Abraham, and the God of Isaac, and the God of Jacob. (Luke 20:37), “Moses showed in [the section on] the bush” (Ex. 3) In Romans 11:22God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying, (Romans 11:2), “the scripture says in [the history of] Elias” (1 Kings 17-19). This may also account for Matthew 27:9-109Then was fulfilled that which was spoken by Jeremy the prophet, saying, And they took the thirty pieces of silver, the price of him that was valued, whom they of the children of Israel did value; 10And gave them for the potter's field, as the Lord appointed me. (Matthew 27:9‑10), where the quotation is said to be from Jeremiah—that prophet being anciently the first in the Book of the Prophets, his name may have been used as a sort of heading.
Most of the quotations are from the Septuagint (LXX), doubtless because it was then better known than the Hebrew, in the same way that the A. V. is now constantly quoted, even where it is not an exact translation. Some quotations are not literally from the Hebrew or the LXX, the Holy Spirit in alluding to them gives them a fullness and power beyond the revelation of the Old Testament.
( In The New Testament Handbook the quotations as they stand in the Hebrew (shown by the AV) and in the LXX (by an English translation) are given in full (G. Morrish, Paternoster Square.) In Horne’s Introduction the Hebrew and Greek text are also given.)
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