This concludes Paul's entire discussion begun in Romans 3:10. The only way we can be justified—that is, have our sins forgiven and be brought into a right relationship with God—is through faith in the sacrifice of Christ. This justification is something that is imputed to us once we meet God's conditions of repentance and baptism (Acts 2:38). We cannot earn it through lawkeeping or doing good works.
However, what many do not understand is that being justified is not the same as being saved. Justification is only one step on the road to salvation. Someone who has been justified cannot break God's laws with impunity and expect to receive salvation anyway. To have our sins forgiven, we must repent from having broken the laws of God (Acts 3:19). To repent means "to turn around"—to stop sinning and orient our lives to obeying God's law. Paul explains it plainly in Romans 3:31: "Do we then make void the law through faith? Certainly not! On the contrary, we establish the law."
The true Christian, having repented from sin, has been given the gift of God's Holy Spirit, which is the love of God that enables him to keep His laws in their full spiritual intent and purpose. He has been justified and has received God's undeserved pardon. He realizes his sins caused Jesus Christ to have to suffer and die. Because of all of these things, the true Christian strives with all his might to resist the pulls of the flesh and to put sin out of his life.
Paul makes it very clear that the true Christian must not continue to live a life of sin. "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it?" (Romans 6:1-2). The true Christian understands that the way he lives and conducts his life has a great bearing upon whether he will inherit the Kingdom of God (Galatians 5:19-21).
To receive salvation, we must not only be justified, but we must live a life of obedience to the laws of God, developing the fruits of His Spirit in our lives (Galatians 5:22-23). Then—and only then—will God give us the gift of eternal life.