Christians generally don't celebrate these Old Testement festivals because they pointed to Jesus and have been fulfilled.
Colossians 2:16-17 tells us they were a “shadow of thing to come" and tells us not to judge each other in keeping them or not.
Jesus was crucified at on Passover
Jesus died and was buried on the Feast of Unleavened Bread
Jesus rose on the Feast of Firstfruits
I think it a very good thing to reflect back on these festivals around Easter, but they were directed to the Nation of Israel rather than the gentiles. God is very exact in how these feasts were to be conducted and there no longer exists a venue to offer burnt offerings of lambs, etc. to Levite priests as it was directed to be done then.