What is a Christian?
A Christian believes in the Trinity: God the Father, his Divine Son, and his equally Divine Holy Spirit. A Christian is one who has personally accepted the substitutionary sacrifice of Christ for sin on the cross and so has been redeemed, born again, baptized in the Holy Spirit, and made one of God's family for the purpose of witnessing to the glory of God and doing the works of Christ.
But I'm a religious person.
Religious observances or actions may be a consequence of becoming a Christian, or salvation, but they are not the cause of it. If one's heart isn't right before God, religious activities make relationships with Him worse, not better. God's word makes it clear that he wants people's hearts, not a veneer of external rituals.
What is Christian Morality?
It can be summed up in two sentences: (1) Know God by faith, learn to love him and his ways, seek to serve him, and have His Holy Spirit instantiate Christ's character in you, and (2) Love your neighbour more than yourself.
Wait. I want to be number one.
Self-fulfillment, self realization, and self-actualization--a three-self philosophy :)--is utterly antithetical to Christianity. Self-ism is a modern (new age) version of hedonism. It cannot lead to God, who will brook no idols, especially self.
How can the world be changed for the better?.
Individuals who accept by faith in Christ the power of God to change them personally are a means by which others also can be changed. Society can only be improved one person at a time from within, and the creator of the universe has sufficient power to do this.
You propose Christian responses to ethical questions. I thought we lived in a post-Christian world.
Perhaps we live in a pre-Christian one.
I don't want Christians shoving their morality down my throat.
Let's put this one to bed for good. Christianity cannot do that, because Christian morality comes from the empowerment of the Holy Spirit working and changing from within, NOT by external force. Besides, there's no shortage of others who try very hard to shove their immorality down other's throats. Rick Sutcliffe's Christian SF has characters who'd like to. Just as Hitler, Stalin, Mao, Amin, real world dictators and persecuters of all eras, such people prove to be a pretty nasty lot.
Hey, man, I'm a moral person. I'm good enough to go to heaven.
The Bible says God's standard for admission is absolute perfection, and that no one but Christ has ever achieved this, because He was God as well as man. So, it's enter on the basis of Christ's merits or not at all. He is the only way, the only truth, the only light.
Variation--You've got your religion; I've got mine.
Strictly speaking, Christianity is not a religion, if by a religion one means a system of beliefs, practices, and rules that is supposed to produce better living, a salvation of some kind, or the reform of person or society. Rather it is a relationship with the living God (initiated by Him) that transforms a person from within.
Variation--I follow the ten commandments. I'll be fine.
The purpose of the Old Testament law was to teach us the impossibility of coming to God by a rule-based morality. It should, as it did with Moses and David, bring us to the point where we realize that law cannot do the job of making a lost human being holy. We can only enter God's presense by His grace.
Jesus was a good teacher. Why say more?
Why do you call Him good? No one is good but God. Jesus Christ not only claimed to be God incarnate, He backed that claim up. Either He was utterly mad, or He was who He claimed to be. A merely "good teacher" explanation doesn't cut it.
How do I become a Christian?
See John 3:3, 16-17; Romans 10:9-11, Acts 16:31. You must confess you are a sinner, unable to enter God's presense on your own merit, and ask in faith that the death and merits of Christ be applied to your account so that you may be born again. God will hear your prayer and give you His salvation by His grace. The death of Christ will be counted as your punishment for sin, and His merits will be used to cloak you in righteousness so that as God looks on you He sees His son. You will become His child and He your Father.
Then, having begun the only possible way, carry on to do. (Holiness is an effect of salvation, not it's cause.) Read the Bible, saturate yourself in the word and obey it. Get baptized. Being immersed does not itself save, but is a public declaration that God has saved you. Actions flowing out of a character that is daily being transformed into Christ's will be evidence you indeed have saving faith.
What should I look for in a church?
You've asked the right question, for you do need to express your Christianity as part of a fellowship of believers, to be discipled and to help make disciples. Look for a church where the Bible comes first, where human traditions and human interpretations are subject to scriptural authority, and where you can see the evidence of God's grace in action as souls are redeemed and lives are changed.
What churches should I avoid?
A Church with heavy emphasis on human leader(s), where the Bible is not regarded as authoritative, with excessive interest in your money, whose elders want to make all your decisions for you, that demands certain works or services to gain a blessing or to earn salvation, or that emphasizes experience, emotionalism (or anything else) above faith, obedience, grace and God's Word. No, we won't be more specific. If you're serious, you can find a good church for yourself. Remember: It's not the name over the door that matters; its the Spirit dwelling in the people who make up the local church that is important.