What is essential to be a Christian? In other words, what are the necessary and sufficient condition that a person with them can be called Christian and without them cannot be called a Christian? What is common between all Christians across the world since the time of Jesus?
I am looking for minimum conditions that whoever satisfies them can be called Christian and a person without them cannot be called Christian. I want to understand the requirements for being a Christian which are common between all Christians, early Christians, Catholic, Protestants, Orthodox, ...