What about different denominations?
The reason there are different denominations within Christianity is because the Bible allows for us to have differences of opinions. Within Christianity there are very few essential doctrines that define what it means to be a Christian. These essential doctrines are,
Jesus is both God and man (John 1:1,14; 8:24; Col. 2:9; 1 John 4:1-4).
Jesus rose from the dead physically (John 2:19-21; 1 Cor. 15:14).
Salvation is by grace through faith (Rom. 5:1; Eph. 2:8-9; Gal. 3:1-2; 5:1-4).
The gospel is the death, burial, and resurrection of Jesus (1 Cor. 15:1-4; Gal. 1:8-9).
There is only one God (Exodus 20:3; Isaiah 43:10; 44:6,8)
God exists as a Trinity of persons: Father, Son, and Holy Spirit. (See Trinity)
Jesus was born of the Virgin Mary (nature of incarnation)
As long as a church believes in these essential doctrines, then it is Christian. However, there are many things in the scriptures that have been interpreted in different ways. For example, what day of the week should be worship on, Saturday or Sunday? Should we baptize by sprinkling or baptize by immersion? Do we take communion every Sunday, once a month, or once a year? The answers to these questions do not affect whether or not someone is a Christian. It is in these issues, and others like them, that denominations are formed. It does not mean that one denomination contradicts another. It means that though they agree in the essentials, they differ in some nonessentials. This is permitted in Scripture:
"Now accept the one who is weak in faith, but not for the purpose of passing judgment on his opinions. 2 One man has faith that he may eat all things, but he who is weak eats vegetables only. 3 Let not him who eats regard with contempt him who does not eat, and let not him who does not eat judge him who eats, for God has accepted him. 4 Who are you to judge the servant of another? To his own master he stands or falls; and stand he will, for the Lord is able to make him stand. 5 One man regards one day above another, another regards every day alike. Let each man be fully convinced in his own mind," (Rom. 14:1-5).
Sadly, there is another reason for denominational differences and that is the failure of Christians to live according to the will of God. The truth is that we are all sinners and we do not see things eye to eye. It is an unfortunate truth that denominational differences are due to our shortsightedness and lack of love. But, the good thing is that God loves us so much that He puts up with our failures. There waits for us, in spite of our differences, a great reward in heaven. Neither salvation nor damnation is dependent upon our differences. Our salvation is based on our relationship with Christ.