Mark had significant influence on the advancement of Christianity. Although the Gospel according to Mark is a narrative of the life of Jesus, theologians consider it to be a handbook of discipleship. The dominant message is that being a Christian is not only believing in Jesus Christ, it is also living according to the example set by Jesus. According to tradition, Mark was the first bishop of Alexandria . One of the most magnificent cathedrals in the world is named after him in Venice , where his relics are kept.