Therefore Let Us Keep the Feast

As a pastor, I have often been asked if Christians should celebrate the seven biblical feasts in Leviticus 23. The common answer is that we don't celebrate the feasts because Jesus fulfilled them. But in Leviticus 23:14, 21, 31, and 41, God said the feasts should be celebrated forever, and in 1 Corinthians 5, Paul wrote, "Therefore let us keep the feast by..." referring to the Feasts of Passover and Unleavened Bread. If God wanted people to stop celebrating the feasts when Jesus fulfilled them, why would He command people to celebrate them forever, and why would Paul say to celebrate them?