Passover, isn't that only in the Old testament?

Yes the book of exodus speaks of the Passover.. but that is the Old testament Passover which Jehovah Commanded to keep at that time. However in the New testament the disciples were commanded to keep the Passover by Jesus Christ. (Matthew 26:17-20; 26-28). The passover from is origination in Exodus... Was a Command we were to keep forever. But why was the way we kept it different because some say only Jewish need to keep it?

“Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished.

Matthew 5:17-18

The reason the order was changed was because Jesus had to come to fulfill the law because it was a law the people couldn't keep (it was way too hard). In the Old Testament the people had to slaughter a lamb and put the blood on there houses. But God was so merciful that he came as the Passover lamb and simply told us to keep it by partaking in his flesh and blood. Seems simple enough!!