God makes clear what sin is in the Bible. It is through sin that we die spiritually; once we become aware of right and wrong, we die spiritually.
9 Once I was alive apart from law; but when the commandment came, sin sprang to life and I died
We are called to obedience by God.
5 Through him and for his name’s sake, we received grace and apostleship to call people from among all the Gentiles to the obedience that comes from faith.
2 Timothy 1:9
9 who has saved us and called us to a holy life - not because of anything we have done but because of his own purpose and grace. This grace was given us in Christ Jesus before the beginning of time
We are saved if we believe what God has done through Christ.
14 Just as Moses lifted up the snake in the desert, so the Son of Man must be lifted up, 15that everyone who believes in him may have eternal life.
16 “For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. 17 For God did not send his Son into the world to condemn the world, but to save the world through him. 18 Whoever believes in him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God’s one and only Son.
But we are saved by grace through faith in Christ.
8 For it is by grace you have been saved, through faith—and this not from yourselves, it is the gift of God - 9 not by works, so that no one can boast.
The Law tells us what sin is, but we are not to sin once we become Christians. We have been set from from sin, to be slaves of righteousness.
20 The law was added so that the trespass might increase. But where sin increased, grace increased all the more, 21 so that, just as sin reigned in death, so also grace might reign through righteousness to bring eternal life through Jesus Christ our Lord.
1 What shall we say, then? Shall we go on sinning so that grace may increase? 2 By no means! We died to sin; how can we live in it any longer? 3 Or don’t you know that all of us who were baptized into Christ Jesus were baptized into his death? 4 We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.
5 If we have been united with him like this in his death, we will certainly also be united with him in his resurrection. 6 For we know that our old self was crucified with him so that the body of sin might be done away with, that we should no longer be slaves to sin – 7 because anyone who has died has been freed from sin.
8 Now if we died with Christ, we believe that we will also live with him. 9 For we know that since Christ was raised from the dead, he cannot die again; death no longer has mastery over him. 10 The death he died, he died to sin once for all; but the life he lives, he lives to God.
11 In the same way, count yourselves dead to sin but alive to God in Christ Jesus. 12 Therefore do not let sin reign in your mortal body so that you obey its evil desires. 13 Do not offer the parts of your body to sin, as instruments of wickedness, but rather offer yourselves to God, as those who have been brought from death to life; and offer the parts of your body to him as instruments of righteousness. 14 For sin shall not be your master, because you are not under law, but under grace.
15 What then? Shall we sin because we are not under law but under grace? By no means! 16 Don’t you know that when you offer yourselves to someone to obey him as slaves, you are slaves to the one whom you obey – whether you are slaves to sin, which leads to death, or to obedience, which leads to righteousness? 17 But thanks be to God that, though you used to be slaves to sin, you wholeheartedly obeyed the form of teaching to which you were entrusted. 18 You have been set free from sin and have become slaves to righteousness.
If we have accepted the work of Christ on the cross for our salvation, we have been set free from sin. We must leave our lives of sin and take on lives of righteousness.