I am a Christian. I believe that Jesus Christ paid the ultimate sacrifice for us when he died on the cross, and I believe that He came back from the dead and lives forever. I believe that the reason Jesus chose to die for us is in the fact that all of us, including me, are sinners. We are missing something in our lives that keeps us from living up to God's perfect standard because in the beginning we chose to turn our backs on Him. Despite that, God loves us enough to give us a way to return to Him, and that is through Jesus.
I believe that to be a Christian, you must first admit to yourself and to God that you are a sinner. Now let me make one thing clear, being a sinner does not mean you are a bad person, nor does it mean you are a good person. We have all done good and bad things, and we would like to think that the good outweights the bad in the end. Sin is something more, something we've been born into. Sin is not what you do, it's who you are, and no matter how good you are you'll never get away from it. It's impossible. It's ultimate end is death and separation from God.
That's where God comes in. He made the impossible possible. He made a way for you to get out of that sin and into God's will. He sent Jesus, His only son, to die on a cross as the penalty for sin. Not just any sin, all sin. The sin of past, present, and future. Not just any person's sin, but every person's sin, past, present, and future. Even yours. Then Jesus rose from the grave to prove His ultimate power over death and sin.
Since Jesus took your punishment for sin, you can be free of that punishment forever. All you need to do is believe in Jesus and what He did, confess your sin to God, and ask Him to forgive you of that sin. It takes faith, but if you do this you can be sure that God will forgive you and take you in as one of His children.
And that's really what being a Christian is all about. It's getting into a father-child relationship with God that is more meaningful than any human relationship can be. Spending time with Him, getting to know Him better, and eventually getting to be with Him forever in Heaven. In all that, however, comes the responsibility to let others know about this great gift.