God created us to have fellowship with him. We, however, have chosen to disobey God and do things our own way. This includes everyone.
God is a holy God and will not tolerate us in this condition of willful disobedience. The punishment for our disobedience is eternal separation from God.
There is hope, however. God sent his son, Jesus, down to earth. Jesus lived a perfect and sinless life. He then gave up his life as a sacrifice so that we may live. He took our punishment on the cross so that we would not have to be eternally separated from God.
So, to be a Christian, means that I must realize that I am a sinner. I must realize that God is a holy God and will not tolerate my sinful condition. I must trust in Jesus to save me from my sins and to pay the price of my sins for me.