John 2:23-25
(23) Now when he was in Jerusalem at the Passover Feast, many believed in his name when they saw the signs that he was doing.

While still in Jerusalem for the Passover Feast, Jesus was publicly ministering and performing miracles. Throughout His ministry, Jesus performed many miracles; most of His miracles were performed for the purpose of establishing His Messiahship and authority over all creation as the Son of God. Many of His miracles served to build saving faith in the individuals who witnessed them. John is not explicit in his description “many believed” as to whether or not this was a saving belief, but the Greek word he uses (pisteuo) means “to have faith in one” or “to entrust one’s spiritual well-being to another (Jesus)” which certainly implies he is referring to people becoming Christian. Not all who witnessed these miracles received this faith, only those who the Father had predestined to salvation. In a similar way, most of the miracles performed by the early church were for the purpose of establishing the church as the holder of God’s authority and was God’s expression of the one true religion in the world. False prophets, false messiahs, and false religions were commonplace. Miracles were one way God chose to distinguish and differentiate Christ and His church from the many false prophets, false messiahs, and false religions of the day. We do not see as many miracles expressed today simply because the legitimacy and authority of the church has been established through the 2000+ years of existence.

(24) But Jesus on his part did not entrust himself to them, because he knew all people
(25) and needed no one to bear witness about man, for he himself knew what was in man.

Here, John gives a subtle but firm testimony of the full deity that Jesus possessed during His earthly ministry. No creation could know all people in this way. “All” most likely does not refer to every single human being on the face of the earth at that time (although that is certainly the case), but all of those people with whom Jesus was in contact during His earthly ministry.