All scripture is given by inspiration of God and is profitable!

Gal 3:8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
I love this verse because it dashes to pieces many erroneous doctrines concerning the difference between the Old and New Testaments.
First we see that it does in fact call an Old Testament passage "scripture". Those who claim that the Old Testament is somehow inferior to the New, or less relevant than the New, do not recognize that they are cutting off the branch they are sitting on. Every New Testament writer consults the Old Testament, or calls it scripture, or uses it as a foundation for their arguments. The apostles would not have accepted Jesus Christ as the Messiah except for the fact that starting in the Law and the Prophets he showed them how the scriptures foretold of him. Peter and Paul could not have convinced the Jews that Gentiles now stood on equal ground with them in the sight of God, except for the prophesies that a day would come when those who did not know God would be called the children of the Living God and the prophesy that there would come a day when a light would be shined on those who walked in darkness. Without the Old Testament the New Testament writers would not have had a leg to stand on, so to diminsh the role of the Old Testament is to diminish the foundation on which the New Testament stands.
Secondly, this verse claims that the heathen were saved by faith, and because of that, God spake to Abraham a Gospel of salvation by faith. Abraham, Adam, Isaiah, the thief on the cross and Paul the apostle were all saved the same way I was... by faith! There can be no argument that the law was the avenue of salvation for the Jews unless we cut Galations 3 out of the Bible. Paul makes a very strong argument, Abraham came before the law so how could the law have saved him? And if Abraham was saved by faith, were the Jews after the law saved differently than faithful father Abraham? (Gen. 15:6 says it was Abraham's belief in God that ws counted as his justification before God.) The law was never meant to save, but to show men that they are incapable of saving themselves and must cast themselves upon the Messiah for mercy.
Thirdly, it says the message spoken to Abraham was "the gospel". The gospel is not unique to the New Testament, the Old Testament saints had it as well. They did not know that His name would be Jesus, but they knew a Messiah would come that would be God incarnate and would save his people from their sins, they knew that He would be God with them, they knew He would be born of a virgin and that it would please God to bruise Him. Even Adam and Eve knew that there would be a seed of the woman whose heel would be bruised by the serpent, yet would ultimatly crush the head of that Old Serpent the Devil.
If ever a man or woman has been saved on this earth, it is only because they believed God and that was counted to them for righteousness. It is only through faith that a sinless Messiah would take their sins and pay their penalty. Thank God that you and I have the New Testament to show us that His name was Jesus, but in the words of our Lord, "Blessed are they who have not seen and yet have believed".