Whosoever believes that Jesus of Nazareth, is the Christ, the Son of God that person has eternal life in him .
Conversely Whosoever does not believe that Jesus of Nazareth is the Christ the Son of the living God, that person does not have eternal life.

1 John 5:10-12
10 He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son.
11 And this is the record, that God hath given to us eternal life, and this life is in his Son.
12 He that hath the Son hath life: and he that hath not the Son of God hath not life.