Romans 4:16 So the promise is received by faith. It is given as a free gift. And we are all certain to receive it, whether or not we live according to the law of Moses, if we have faith like Abraham’s. For Abraham is the father of all who believe.
17 That is what the Scriptures mean when God told him, “I have made you the father of many nations.” This happened because Abraham believed in the God who brings the dead back to life and who creates new things out of nothing.
18 Even when there was no reason for hope, Abraham kept hoping—believing that he would become the father of many nations. For God had said to him, “That’s how many descendants you will have!”
19 And Abraham’s faith did not weaken, even though, at about 100 years of age, he figured his body was as good as dead—and so was Sarah’s womb.
20 Abraham never wavered in believing God’s promise. In fact, his faith grew stronger, and in this he brought glory to God.
21 He was fully convinced that God is able to do whatever he promises.
22 And because of Abraham’s faith, God counted him as righteous.
23 And when God counted him as righteous, it wasn’t just for Abraham’s benefit. It was recorded
24 for our benefit, too, assuring us that God will also count us as righteous if we believe in him, the one who raised Jesus our Lord from the dead.
25 He was handed over to die because of our sins, and he was raised to life to make us right with God.
Here it seems, that Paul is using Abraham as a positive support for his own position in Christ. The Jews of his time, were avid followers and believers of Abraham. For the Jew of this time, Abraham is considered the father of the Jewish Nation. However, Paul uses the faith of Abraham to get his message across to those that have drifted away from the faith, and have become law minded and law driven. The law has become a Nehushtan to much of the Jewish population (read Numbers 21 and 2 Kings 18). The law was imperfect and becoming more imperfect over time, due to the meddling of man. Abraham followed much of the laws (Genesis 26:5), but not because he was law-minded. Rather, Abraham was God-minded, and what God told Abraham to do, Abraham did it because he had a reverence for God. Much like those of us who obey God today. I cannot speak for others, but as for me, I follow what God says because I know that God knows best. I have tried it on my own and failed miserably. I know that when God tells me to do something, it is for my own good in the end. I have found that what God says is truth. Took some hard knocks, but thank God this gal has SOME semblance of good sense. And to God be the glory for that!
Paul was using Abraham as an example of what the Christian faith is about. Abraham is the father of Christians, not necessarily the father of the Israelites. It is by faith one is justified, not by the law. Faith in Jesus Christ as Lord and Savior. Faith in the blood of Jesus. Faith in the resurrection of Jesus. Faith in the Divinity of Jesus. Faith in the believing that what God said God did and .. God did indeed, send His One and Only Son to restore mankind to Him.
Paul was telling the Jew of his time, that Abraham was the father of the Chrisitan believer. Not the father of the circumcised Jews of the law.