John 2: 18-25, Destroy This Temple

Jesus clears moneychangers, sheep and cattle out of the temple grounds in Jerusalem. After doing that, he is challenged by temple leaders.

John 2: 18-22, Rebuilding the temple in 3 days
The Jews then responded to him, “What sign can you show us to prove your authority to do all this?”

19 Jesus answered them, “Destroy this temple, and I will raise it again in three days.”

20 They replied, “It has taken forty-six years to build this temple, and you are going to raise it in three days?” 
21 But the temple he had spoken of was his body. 
22 After he was raised from the dead, his disciples recalled what he had said. Then they believed the scripture and the words that Jesus had spoken.

Jesus is challenged as to the reason for his actions in the temple and responds with a messianic statement. This statement about rebuilding the temple is later twisted by Jesus's accusers to be an attack on Judaism.

John 2: 23-25, Feast and fickle followers
Now while he was in Jerusalem at the Passover Festival, many people saw the signs he was performing and believed in his name.
24 But Jesus would not entrust himself to them, for he knew all people. 
25 He did not need any testimony about mankind, for he knew what was in each person.

The author of this gospel will consistently emphasize belief and people's response to the actions and teaching of Jesus.  Here we are told that "many... believed" because of the "signs" he performed. Both the actions at the Cana wedding and the reaction to the moneylenders are signs of Jesus' authority as Messiah.

These signs "testify" about the identify of Jesus, but as to the identity of mankind, no testimony is required!  We will be reminded again and again that Jesus, the True Light (as described at the beginning of the book), is very aware of how fickle we humans can be.  The people are impressed by miracles but pay more attention to the entertainment than to the One working the miracles.  Throughout John's gospel, many miracles comes with a statement, an explanation of purpose, not of entertainment.