“But Jesus was speaking
Of the temple
Of his body.”
ἐκεῖνος δὲ ἔλεγεν περὶ τοῦ ναοῦ τοῦ σώματος αὐτοῦ.
Only John uniquely gave an explanation about the rebuilding of the Temple. Of course, Jesus was speaking (ἐκεῖνος δὲ ἔλεγεν) about the temple of his body (περὶ τοῦ ναοῦ τοῦ σώματος αὐτοῦ), not the Jerusalem Temple that was destroyed in 70 CE. His body would be resurrected on the third day. John felt it necessary to explain this saying, while the canonical synoptic writers only implied it. Is your body a temple?