While the Jews wondered if there was any value to being chosen by God, Paul not only said there was, but that the value was from God’s perspective, and not mans. God chose Abraham for His purposes and, significantly enough, Abraham antedates Israel. Abraham was (is) the father of the faithful, but his recognition as being the father of the faithful was a long time before even Moses existed. What set Abraham apart was his response to the Lord – even before he received the physical sign of circumcision (God’s seal). The importance of this is with regard to salvation under the new covenant. Jesus came to save all those who call upon His name; it won’t be only Jews who call upon His name, but non-Jews as well. Thus, the standard of righteousness (faith) put forth for consideration is Abraham. In fact, if one would be justified before God, then Abraham is a great example (4:18-21) to emulate.
It is important to keep in mind the context of the word “works” in this chapter (as well as in every/and all chapters). When the author makes use of the word, it is imperative that one get a proper sense of what is in view. Three times Paul makes use of this word in the chapter (4:2, 4, and 6). In 4:2, he uses the word in relation to 3:28 (works of the law, i.e. Law of Moses). In 4:4, he uses it in a more general sense, but its relation to 4:2 can’t be missed. And in 4:6, he uses it to contrast what is important in one’s spiritual walk between the works of the law or God counting one righteous. So, when the Scripture says that Abraham was not justified by works, those works pertain to the Law of Moses.