John 2:19-21
Jesus answered them, “Destroy this temple, and in three days I will raise it up.” 20 The Jews then said, “It has taken forty- six years to build this temple, and will you raise it up in three days?” 21 But he was speaking about the temple of his body.
John 20:6-8
Then Simon Peter came, following him, and went into the tomb. He saw the linen cloths lying there, 7 and the face cloth, which had been on Jesus ‘ head, not lying with the linen cloths but folded up in a place by itself. 8 Then the other disciple, who had reached the tomb first, also went in, and he saw and believed;

Revelation 21:22

And I saw no temple in the city, for its temple is the Lord God the Almighty and the Lamb. 

     Any doubt whether or not Jesus was serious when he made the above prediction is dispelled by the resurrection and John’s vision in Revelation. The Jewish leaders did not understand him, the people did not understand him, the disciples did not even understand what he could possibly mean that he would rebuild the temple in three days.  After the resurrection, the disciples understood.  After the 2nd resurrection we (followers ofmChrist) will see the only temple that is necessary for all eternity, the Lamb of God who takes away the sins of the world.