Because you will - everyone dies.
Theology, in general, is the study of God. For individuals, it is our personal god. Christians endeavor to conform their notions to the true God, as revealed in the Bible.
On Sunday, July 27, 2008, a man with very evil and twisted beliefs killed people at a Unitarian Universalist (UU) church in Tenessee.
This is a sad and tragic story, which I want to handle with sensitivity and tact...
But, this is what the UU church believes (from their website):
"WE BELIEVE in the authority of reason and conscience. The ultimate arbiter in religion is not a church, nor a document, nor an official, but the personal choice and decision of the individual."This is what that man believes (from the affidavit at Wikipedia):
"he had targeted the church because of its liberal teachings and his belief that all liberals should be killed because ...[no good reason]"Personal choices can be wrong. Evil people will justify themselves, and do evil. This man believed he should kill people with sufficient vigor to actually do it.
There must be a standard of good and evil. That standard is outside of our personal choices and decisions. For Christians, that is the Bible. The church is a group of people meeting together and agreeing on how to teach from the Bible. The officials in that church are approved (and, I'm pretty sure, appointed) by their members to be teaching them.