Albert Barnes on John 9:35

Dost thou believe on the Son of God? Hitherto he had understood little of the true character of Jesus. He believed that he had power to heal him, and he inferred that he must be a prophet, Jn 9:17. He believed according to the light he had, and he now showed that he was prepared to believe all that Jesus said. This is the nature of true faith. It believes all that God has made known, and it is prepared to receive all that he will teach. The phrase Son of God here is equivalent to the Messiah. Mt 8:29.

(x) "believe" 1Jn 5:13