This is a claim made by Jesus, which almost nobody understands at first. In Jewish society, the temple in Jerusalem was the most important place. Therefore, when Jesus claimed to be able to rebuild a destroyed temple in only three days, they regarded Him as crazy. As a matter of fact, Jesus was referring to His own death and resurrection in the future. It will become evident to the disciples after He has been crucified.
God ordained the beautiful Temple in Jerusalem to be a temple of prayer for all nations. However, the religious leaders became proud and rebellious, and rather than being used for its hallowed purpose of worship and prayer, the holy Temple of God became a place of ungodly merchandise, dishonest trading, and gross malpractice.
As He hung on the cross and shed His blood for our sins as well as theirs, there were also those who recalled His words and mocked Him. His temple was destroyed, but through death, He defeated the one who held power over death, namely the devil, and in three days, He rose so that all those who believe in Him may not perish but have everlasting life.

Dear Heavenly Father, it is Your only Begotten Son who took on human flesh and became a member of the human race and showed us the way to life everlasting. Thank You for making my body a temple of the Holy Spirit and indwelling me with His Spirit by faith in Him. In Christ's resurrection, death no longer has dominion over me, and I am alive in a new way. The day will come when I will also be clothed in a resurrected body. 
In Jesus's name I pray. Amen.