Sin is a transgression of the law of God (I John 3:4). Sin can be seen as something we do as in a one time act or something that we live in, daily. Paul wrote about Gentiles and how they lived in sin before they became Christians (Col. 3:7). This refers to living in sin. John warned against a person saying that they had no sin (I John 1:8). This refers to a one-time act of rebellion against God. Sin when committed must be faced by the sinner and dealt with according to the law of God.
Those who are outside of Christ are dead in their trespasses and sins (Eph. 2:1). They must come to spiritual life by accepting the truth and obeying that truth. When the truth is obeyed, the heart is purified (I Peter 1:22). Such purification comes about because one has contacted the blood of Christ in baptism (Rom. 6:4; Col. 2:12). Once purified by obeying the truth, the Christian continues to live his life for God (I John 1:7). When he sins, he must confess and seek God’s forgiveness through prayer from a proper mind set of heart (1 John 1:9). God will forgive.
Are some sins greater? Jesus in His conversation with Pilate made this observation about Judas. The one who delivered Me to you has the greater sin (John 19:11). Was Pilate wrong for giving in to the crowd instead of doing what was right? Yes, he was. Jesus was stating that Judas had a greater sin than Pilate. The wages of sin is spiritual death, that is separation from God for all eternity (Rom. 6:23). Any sin or sins that we do not get out of our lives has the potential of costing us our salvation. I would also add that some sins have a greater consequence. We can obtain forgiveness but that does not necessarily remove the consequence of our actions. So yes, some sins are greater than others.