Romans 4: 1-8:

What then shall we say was gained by Abraham, our forefather according to the flesh? ² For if Abraham was justified by works, he has something to boast about, but not before God. 

If Abraham was justified by works, there would be no need for faith. If we could be forgiven just by doing "good" acts, there would be no need of true repentance as long as you do a good deed after a sin to justify you.

 ³ For what does the Scripture say? “Abraham believed God, and it was counted to him as righteousness.”

Here it says clearly that he believed God, and that belief counted as righteousness. Faith is more powerful than "good" works.

⁴ Now to the one who works, his wages are not counted as a gift but as his due. 

If you work, your paycheck isn't considered a gift, it's considered your due. If you don't work for it, and it's given to you, that's when it's a gift.

 ⁵ And to the one who does not work but believes in him who justifies the ungodly, his faith is counted as righteousness, ⁶ just as David also speaks of the blessing of the one to whom God counts righteousness apart from works:

He who believes will be counted as righteous, because he believed in God.


 

⁷ “Blessed are those whose lawless deeds are forgiven,
    and whose sins are covered;
⁸ blessed is the man against whom the Lord will not count his sin.”

Whoever sin is forgiven, that person is blessed... If you believe and are counted as righteous, you are blessed.

Romans 3:21-31 (ESV)

The Righteousness of God Through Faith

²¹ But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— ²² the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: ²³ for all have sinned and fall short of the glory of God, 

 Everyone can be cleansed through faith in Jesus, you just got to believe. We all sin, so we all fall short of His glory.

 ²⁴ and are justified by his grace as a gift, through the redemption that is in Christ Jesus, ²⁵ whom God put forward as a propitiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins.

 Because Jesus died, we are forgiven by his blood.

  ²⁶ It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus.

 In His righteousness, and His mercy, He has now given us the lamb we need for our sins to be washed away for good. You just got to believe in Jesus and you will be justified.

²⁷ Then what becomes of our boasting? It is excluded. By what kind of law? By a law of works? No, but by the law of faith.

 Our works is nothing to boast about, our works, our good deeds, are like dirty rags. By our faith, we are saved.

  ²⁸ For we hold that one is justified by faith apart from works of the law. ²⁹ Or is God the God of Jews only? Is he not the God of Gentiles also? Yes, of Gentiles also, ³⁰ since God is one—who will justify the circumcised by faith and the uncircumcised through faith. 

 God is God of all, not to just one nation, but to ALL the nations.

 ³¹ Do we then overthrow the law by this faith? By no means! On the contrary, we uphold the law.

By this faith, we will keep the law, we will want to do what is pleasing to God, so we will keep this law because we want to.