Abraham believed the Lord
Continuing on with the argument or the case that we are saved, not by our own works, but through faith, we are now presented with an example. We are presented with Abraham - the Jewish patriarch. Paul points back to a really key verse from Genesis:
Abram believed the Lord, and he credited it to him as righteousness. (Genesis 15:6)
We can not boast about our own religious accomplishments, even Abraham... even Abraham was justified (made righteous) by faith. Paul has phrased it as a question to help us think about this even more. He's saying, "here is my point - not works, faith... and here is the example"
Abraham is the key example. Paul is saying if this is true for Abraham then what Paul is saying is true for us too. The story of salvation is true and documented through the holy scripture. Abraham is therefore evidence (in this sort of court case), that Paul's theology (point of view) is correct. That Abraham is the model of faithfulness over works. This also pulls the Old Testament (the Jewish story of salvation) together with the saviour - who is Jesus. And links it back to salvation being open to all the nations - as Abraham was to be a blessing to all the nations.
Genesis 15:6 is therefore a key verse and is also quoted in Galatians 3:6. Abraham's faith is in response to God's promise to make the descendants of Abraham as uncountable as the stars in the night sky. The impact of this is reduced through our lives in the city and the yellow light glow cities produce. If, however, you've ever been out and away from the city on a clear night, you are unable to count the stars against the pitch-black sky.
The story of Abraham is surrounded and built on the promises of God and the covenant that God made with Abraham. The covenant that promises to make Abraham a great nation, to magnify and bless him and in turn for him then to be a blessing for all peoples on earth. For many nations to come from Abraham. As a result, God institutes circumcision as a sign of this covenant. The descendants will come from Abraham and Sarah, however, they are old and the first test (which they fail) is they're to trust God to fulfil on His promise. They instead attempt to solve their own problem of childbirth. However, they are finally blessed with a miracle, a miracle that only God could do - they have Isaac. Abraham is tested again when he is asked by God to sacrifice his son. This time he doesn't fail, however, God stops him at the last moment, replacing Isaac with a ram. This is Abraham's trust in the Lord and His promises. Abraham's life shows us that believing God is how we become righteous in His eyes. That is, that we may be 'right' before God.
We are then exposed to a detailed breakdown of what Paul means by this idea of credited. Our works are not credited to God, but rather come as a result of being obedient to God. When we 'work' in our job, the employee pays us a wage. This is not a gift, but rather an obligation on the employer to pay you. This is not the case with God. God can't break who He is, because He would then be giving people something they had earned. Christians, therefore, don't base their relationship with God on their actions. God is a God of grace who always gives freely and without constraints. He can never be obligated to any person and therefore God can not 'credit' humans on the basis of their works.
We are then introduced to a second example, David, and his words found in Psalm 32:1-2. These also use this idea of credited. People who are blessed are not those who have earned something from God, but rather those who have received something from Him. Transgressions have been forgiven and our sins, covered.
The wicked are declared innocent, not because they have earned it, No, in fact, we don't deserve it at all - this is grace! This is the Good News. Jesus has changed our status before God. When we are 'in Christ' we are credited with His perfect righteousness. We must be careful with this truth. We can't afford to practice 'cheap grace'. It doesn't mean we are 'let off the hook' and can continue in our sinful ways, transgressing against God. But rather when we are 'in Christ' our worship follows, our service, our obedience, and our stewardship of all that we are given - is for the Lord. We are to pursue holiness.