There is only one way of salvation for mankind in time and space. This way of salvation is not through works, but it is through faith. The Old Testament church was not saved by the keeping of the law. Moses certainly did not ever teach salvation by works. Nor was Israel saved by keeping the sacrificial system and offering the gallons of blood and fat to the Lord. Rather the only possibility of salvation is found in Jesus Christ. It is only by faith in Jesus Christ that man is saved.
That salvation is only found in having faith in Jesus Christ is the clear teaching of Genesis 15:6: “And he [i.e. Abraham] believed in the Lord, and He accounted it to him for righteousness.” This statement is very significant in the historical narrative of Genesis. Indeed, as Keil remarks,
In the strictly objective character of the account in Genesis, in accordance with which the simple facts are related throughout without any introduction of subjective opinions, this remark appears so striking, that the question naturally arises, What led Moses to introduce it? In what way did Abram make known his faith in Jehovah? And in what way did Jehovah count it to him as righteousness?
The answer to these questions, as Keil points out, is found in the immediate context of Genesis 15. Abraham brought the heifer, the goat, the ram, the turtledove, and the pigeon in obedience to the command of the Lord. He shed the blood of these animals when he divided them in half. He watched when the Lord passed through the midst of them, as a sign and a seal that the Lord Himself and no other was the author and the executor of this covenant. Further, in the shed blood of these animals, the Lord was symbolizing how He was going to bring about the reality of this covenant: the sacrifice of the seed prophesied in Genesis 3:15. Moses then introduces this beautiful phrase to demonstrate that Abraham’s salvation was not of his own doing, rather it was his belief and confident trust in the promises and the covenant of the Lord. The content of which was that He would bring about redemption through Abraham’s seed. It was then this belief in a coming savior that the Lord accounted as righteousness to Abraham.
The Apostle Paul, in his divinely inspired commentary on this passage in Romans 4 sheds some light on what it means that the Lord accounted his belief as righteousness. Paul makes it utterly clear that Abraham was not justified by the works of the law or by circumcision. Indeed, Abraham was accounted as righteous before he was circumcised in Genesis 17. Righteousness can in no way be earned through the law, because the law brings about wrath (Rom. 4:15). It is the law that condemns a man. Not even the promise that Abraham and his seed would be heirs of the world was through the law (Romans 4:13). Rather, the promise of the inheritance and the imputed righteousness is of faith by grace (Rom. 4:16). That is, salvation is by faith in the grace, the undeserved favour, of God. God grants righteousness not to the one who works, but to the one who believes in the gracious redemption of God (Romans 4:5).
The blessedness of this is not only that salvation is a work of God’s grace alone, but it is also a universal salvation. To be clear, that does not mean that everybody is saved head for head, nor does it mean that Christ has died for everybody. Rather, it means that salvation is not for one specific ethnic group (e.g. the physical descendants of Abraham), but salvation is open to all nations. Salvation is for those “who are of the faith of Abraham, who is the father of us all” (Rom. 4:16). This is the blessed theological significance of Genesis 15:6.
 All Bible quotations taken from The New King James Version (Nashville: Thomas Nelson, 1982)
 C.F. Keil,, Commentary on the Old Testament Volume 1: Pentateuch, (Massachusetts: Hendrickson Publishers, 2011), 135