What makes someone a Christian?

There are many people who state that they are Christians. However, what does that mean? What does it mean to be a true Christians? The modern understanding of religious expression dictates that this is practiced on an individual level. Therefore, many believe that their individual prayer at home, away from the embrace of the Church is the way forward. However, this is quite wrong, going against the theology, practice and Tradition of the Orthodox Church. Christos Yannaras, in his book The Freedom of Morality, claims:

‘What makes someone a Christian is not his private virtue or ideas or convictions, but the fact that he participates organically in the life-giving body of Christ, being grafted into the liturgical unity of the Church. Sin is what cuts man off and alienated him from the body of the Church: virtue is what brings him in and grafts him into the “good olive” of grace.’ (p.83).