When they saw him driving out the money changers and heard him castigating them, the disciples remembered the line from the Psalms, "Zeal for your house will consume me." Jesus was willing to challenge those who were using for their own benefit what was to be a place to worship.
Jesus said, "If you destroy this temple, in three days I will raise it up."
By the time that John's gospel was written, this temple had been destroyed by the Romans in retribution for a Jewish insurrection.
Christians began to understand Jesus' words as telling them that he, his living presence, would be the temple for them.