Chapter Three presents Paul’s logic of the Law. Again, he admits a good to the law and circumcision. God’s goodness is not nullified because of the law, nor is His justice because of grace. The punishment from God does not make Him a tyrant. God is just and ought to exact justice. How many of us would complain when justice is not served to someone who has done wrong to us? Yet how many of us would complain if justice is given to us when we have wronged others? Justice is a two-way street. We never look to ourselves and our own actions. Yet all this justice does not mean that God is not merciful.  
All that being said, does God enjoy exacting punishment? No. God really does not have to actively punish us anyways. As said in Chapter One, God leaves us to our own design. The fruit of our sins will always come back to bite us. It is the nature of sin to cause the sinner to suffer. If we do not want God in our lives, then He makes His absence happen. He does not impose His goodness on us. It is all based on, for lack of better terms, the nature of who God is. What is this nature? Goodness itself. God is goodness itself. Anything opposed to this goodness is opposed to God. When goodness is absent, humanity suffers.
We are all under the yoke of sin, Jew or Greek (v9). What Paul is getting at here is that no matter where you are from, every human being in the world is under the yoke of sin. We are all sinners. The law makes us more conscious of our actions in morals (v20). The law teaches us of God’s ways and how to be good and to avoid evil. So the law is good. Since all human beings are subject to sin, we are in need of God’s grace equally (v23-24). But the grace of Jesus’ blood proves God’s goodness (v25). We have access to God’s mercy and the forgiveness of sins through His blood and our faith in Jesus. So without faith, we cannot attain eternal salvation. Faith is absolutely necessary.
There are some assumptions about faith that open us to salvation. First, faith implies that we trust in God. This trust assumes that God wants what is good for us. God has no evil in His heart and would never deceive us. Second: that God loves us. If we do not trust God, we are doubting that God actually loves us. Jesus dying on the cross is the proof we need that He really does love us. Third, that we love God. It is hard to love a person whom we do not trust or believe in. But Scripture says, “even the devils believe” (Jas 2:19). Those in hell believe in God, they just hate Him. But if we believe that God is trustworthy and loves us, we ought to love Him back. Fourth: that a relationship is enjoyed. The faith we have in God is not that of some thing; I trust that my printer will print the page I want when I tell it to. It is a faith in persons, three persons to be exact, Father, Son and Holy Spirit. These three persons have entered our lives and bring us grace to every part of our lives. Fifth: that faith itself is a gift. God gives us the gift of faith. We cannot get faith for ourselves or purchase it by any means. God freely gives it to all who would accept it. We have to be willing to accept it and do so. Our actions play a part in this acceptance of Faith in many ways. A book could be written on this alone. Sixth: faith is integrated. The entire person is involved in faith. It incorporates body and soul. It involves all the powers of the soul: the intellect, passions and the will. How are you doing in all these assumptions of faith?
Works cannot provide for grace no more than the natural can provide for the supernatural. Works are natural and mere human. Grace and faith is supernatural and come from the divine. Grace can build upon works, but works by themselves can only do so much by themselves. With that in mind, works cannot give us sufficient reason to boast (v27), but faith in Him can give a reason to rejoice.