Summary: We can grasp that the Old Testament is confirmed by the New. But how is the New confirmed?
4. Testimony to New Testament Inspiration
God used forty different men over a period of 1,600 years to complete His written work. He used a butler, a scribe, kings, a doctor, a theologian, fishermen, a statesman, a farmer, a tax collector, a Pharisee.
Someone has calculated that there are 320 quotes in the New Testament from the Old. But what of the New itself? So far, most of what has been said above refers to the Old Testament Scriptures. Obviously the Old Covenant, as we know it, was the full Bible in apostolic days. But things were changing. God was adding a new section to His Book, a record of a new covenant, prophesied by Jeremiah and others (Jeremiah 31:31), enacted by Jesus, and spelled out for us by apostles, historians, theologians and prophets, in a book we now call the New Testament. How does the New Testament "prove" itself to be true? Here are some evidences:
For this reason we also thank God without ceasing, because when you received the word of God which you heard from us, you welcomed it not as the word of men, but as it is in truth, the word of God, which also effectively works in you who believe.
An apostolic word is spoken, and now written, to the Thessalonian Church. The Thessalonians receive it as from God. And so do we. By implication, we receive all the epistles of Paul in that same vein. By even broader application, we allow all genuine apostolic letters and histories and prophecies, the authority they are due.
For the Scripture says, "You shall not muzzle an ox while it treads out the grain," and, "The laborer is worthy of his wages."
Here Paul, in describing what ought to be our attitude in supporting those who teach us, quotes two “Scriptures.” The first is from Deuteronomy 25:4, the second from the Gospel of Luke, 10:7. Paul seems to be equating what was given by Moses with what was said by Jesus and given us by Luke, a traveling companion of the apostle.
For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord will by no means precede those who are asleep.
This is one of many such texts. Paul is not hesitant to declare that when he speaks, he speaks by “the word of the Lord.” See also, for example,
Now the Spirit expressly says that in latter times some will depart from the faith, giving heed to deceiving spirits and doctrines of demons,
Again, no question as to Paul’s source of authority and verbage. He listened long to the Holy Spirit, and wrote what he heard.
If anyone thinks himself to be a prophet or spiritual, let him acknowledge that the things which I write to you are the commandments of the Lord.
Doesn’t get any plainer than that. The Lord spoke to apostles as He did to prophets, and their words are to be obeyed. Period.
14 Therefore, beloved, looking forward to these things, be diligent to be found by Him in peace, without spot and blameless; 15 and consider that the longsuffering of our Lord is salvation--as also our beloved brother Paul, according to the wisdom given to him, has written to you, 16 as also in all his epistles, speaking in them of these things, in which are some things hard to understand, which untaught and unstable people twist to their own destruction, as they do also the rest of the Scriptures.