Sin comes from unbelief, and includes: 1. all unrighteousness (right=faith) 2. when you know do good and don't. 3. whatever is not done in faith
Those that think they have no sin, are decieved. Because we committed sin, we haven't seen nor known God, but are chidlren of disobedience, the devil, and God's wrath as others. We are sold under sin. Sin dwells in us and we in it. And some die in sin. (The righteous dwell in Christ and He in them, die in Him.)
The devil sins from the beginning. Sin is against God, mostly. Sin came into the world, bringing death. So the devil had this power. But Christ appeared to destroy the work of the devil. Death no longer has dominion over Christ. He has condemned sin in the flesh.
Jesus was seperated from sinners, knew no sin, and did no sin. He was without sin.
He was made a sin (or sin offering) for us. Jesus is the sacrifice, offering to God, and propitiation for sin. In His flesh/body and cross, He bore (the responsibility) of our sins. (Like He bore the infirmities of all of the many who came.) He gave HimSelf for sin. Jesus suffered unto death and died because of sin. He made reconciliation. Jesus saves sinners.
The law was provided for those who serve sin. The law gives us knowledge of sin. Sin is the transgression of the law. And sin get's it's strength from the law. The law was temporary to lead us to Christ.
God says you're a sinner so: confess and repent of sins. If sin advocate. God's always faithful to forgive believer's sins. Reading the Bible helps us not sin.
For us who walk in the light, and after the Spirit rather than the flesh: Jesus made his appearance here to forgive, remit, take away, purge, blot out and no longer remember our sins. He washes away our sins and cleanse us with His blood. Forgiveness=redemption. He lays not the charge of, He doesn't impute sin to us. Our sins are covered from His sight.
The deceiving pleasure of sin easily beset us. No longer let sin reign/have dominion in your mortal body, through lust. Lusts corrupt the world. But we're free from and dead to sin so we can live for Him. Those who are born of God or abide in God don't sin and can't sin because they are God's seed the devil can't tempt them. If you walk in the Spirit, you'll not gratify your fleshly lusts. We strive against sin and are opposed by sinners, like Jesus. If your flesh suffers, you're done sinning.
2Co 5:15b-16 ...he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again. Wherefore henceforth know we no man after the flesh: yea, though we have known Christ after the flesh, yet now henceforth know we him no more.
Rom 14:9b...to this end Christ both died, and rose, and revived, that he might be Lord both of the dead and living. (...belong to Him)
Luk 24:46b behoved Christ to suffer, and to rise from the dead the third day:...that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.
Short:
The devil sinned from the start, and uses our lusts and unbelief to get us to sin to death. The law showed sin in us and us sold in it. So Jesus came to destroy this work of satan. In His body Jesus condemned sin, releasing us from it. He had taken the responsibilty for our sins, not just our sicknesses.