The last supper Jesus had with his disciples before his crucifixion was a celebration of?

It was the Passover - a memorial of the sacrifice of Jesus Christ, "our Passover," which made possible the forgiveness of sins - by human blood we all have sinned and by human blood we all are forgiven:

1 Corinthians 5:7New King James Version (NKJV) 7 Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us.