(1) to believe that Jesus was born, lived, died, and was raised from the dead?
(2) to accept that God became a man in the person of Jesus Christ in order to reconcile all men with Himself?
(3) to receive Jesus and have a personal relationship with Jesus Christ?
Option #1 - has to do with the historical Jesus and the events of His life in the first century.
Option #2 - has to do with the theology of Jesus which explains incarnation and Christology.
Option #3 - has to do with the personal, subjective experience of Jesus.