The simplest way to answer this question is to point out that Christianity as a religion is fundamentally based on the teachings of Jesus of Nazareth. The most basic idea, more or less common to all Christians (though not necessarily early Christians) is that Jesus was the Son of God, sent to earth, where he attempted to offer men a means to spiritual salvation, and, to a large extent, a path to earthly happiness. He was crucified and buried, and, according to Christian theology, rose from the dead and physically appeared to several people before ascending into heaven. His death, according to Christian theology, provided salvation to Christians by washing clean the sins of all who believed in him. In many ways, Jesus embodied the body-spiritHis moral philosophy, based on love and forgiveness, is also held up by Christians as a guide for living. So in short, Jesus is absolutely essential to Christianity.
Jesus is so important to Christianity because His blood was shed for the purpose of salvation. He was sent as our Redeemer and Savior and through Him the world might be saved. Without these factors for His coming, Christianity would not be present. In others words, He is the Christ which is the root of Christianity and following Him is just as important as He is to Christianity.