One possible explanation:
(John 2:19) "All right," Jesus replied. "Destroy this temple, and in three days I will raise it up." (NLT)
(Ephesians 2:21) "...in whom the whole building, being fitted together, grows into a holy temple in the Lord.."
Jesus had spent the previous three years establishing a spiritual arrangement concerning the New Covenant which he was about to validate with his death. When he died, (the cornerstone - Eph. 2:21) his followers (the "temple") were distraught and dispersed, but on his resurrection, Jesus had them regroup with an even stronger zeal than before. Hence his reason for saying that he would "raise it up" (Gr.egeirÅ - "to cause to appear, bring before the public")