John 14 v
1 Let not your heart be troubled: ye believe in God, believe also in me. 2 In my Father’s house are many mansions: if it were not so, I would have told you. I go to prepare a place for you. 3 And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also.4 And whither I go ye know, and the way ye know.
After Jesus had healed the man who was blind from birth he asked him if he believed in the Son of God:
Jesus Heals the Man Born Blind
John 9 v
1 And as Jesus passed by, he saw a man which was blind from his birth. 2 And his disciples asked him, saying, Master, who did sin, this man, or his parents, that he was born blind? 3 Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him. 4 I must work the works of him that sent me, while it is day: the night cometh, when no man can work. 5 As long as I am in the world, I am the light of the world.
35 Jesus heard that they had cast him out; and when he had found him, he said unto him, Dost thou believe on the Son of God? 36 He answered and said, Who is he, Lord, that I might believe on him? 37 And Jesus said unto him, Thou hast both seen him, and it is he that talketh with thee. 38 And he said, Lord, I believe. And he worshipped him. 39 And Jesus said, For judgment I am come into this world, that they which see not might see; and that they which see might be made blind.
To be a Christian we must commit the gravest sin possible in the eyes of the islamic religion, and that is to associate the Son of God with God the Father and worship both together as one God.