The plain gospel is more simple, and more terrifying, than most of us have imagined. Simply, God created and owns every person. As such, you are bound to obey God perfectly. However, you've rebelled against God. Now, his penalty of eternal death is against you. Because God does not take pleasure in the death of the wicked, he sent his Son Jesus Christ to provide a way of escape for those who will forever leave all rebellion and devote the rest of their lives to perfectly love and obey God.
But the gospel doesn't end there. Once a person repents, receives the Holy Spirit, and is made holy, he must never sin again. Most boldly, Hebrews 6 states,
For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame. (4-6)
If you say you are a Christian and are in sin today, it's for one of two reasons. One, it is because you never truly repented. You never forsook all sin and totally submitted to Jesus Christ. Second, it is because you did repent, and God did make you holy, but then you willingly turned away. In either case, you are in terrible danger. Will you immediately fly to Christ, and cry out to God to have mercy on you?