Religion questions regarding the covenant and passover in gospels of luke and john?

Jesus communicated using these symbols because God originally ordained Passover, the feasts, and the covenant to point to Jesus as the coming Messiah. Thousands of years ago God required that Israel paint the blood of the lamb over the doorposts in their homes in order to avoid the judgement of God. The israelites painted their doorposts with the blood of a lamb and the punishment of God came upon the Egyptians.

Jesus is our lamb. We symbolically claim his blood as atonement for our sins to avoid the judgement of God. He had to die so that we can live. Jews in Jesus day would have been as familuar with passover as we are with fourth of July. They would have known and been abel to connect the dots much easier than we can. As Paul said... the law was the tutor pointing to Jesus christ. In Collosians 2 Pauls says that the law is a shadow of things to come (Jesus). Jesus was proving he's the Messiah when he said, "this is my blood, take and drink..." And again when he said "This is my body, take and eat" He did this when he brok teh bread letting us know that he was the passover lamb which lets us escape the punishment of God.

Because Jesus was Jewish. The sympbolisms and traditions were familiar to Jesus and those he was teaching. You have to remember that Christianity did not exist until Jesus was recognized as being "the Christ".