God first revealed himself to Moses in the burning bush. Moses answered God's call reluctantly. He and Aaron went into Egypt to face the people he once knew well. God wanted to send a strong message that HE and HE alone was God. So, he sent plague after plague combating the gods of the Egyptians. He turned the Nile into blood. This sent a message to there god and goddess of the Nile [Hapi & Isis]. Only Moses could turn the blood back into water. Each plague challenged one of their gods. Finally God knew that to get his message through he would need to do something that would send his message loud and clear. So, that is when Moses warned him that God would take the first born son of anyone that does not smear the blood of a lamb over the doorpost of their house. Every Israelite did this and the Lord passed over those houses. Ultimately it took the life of Pharaoh's oldest son. Pharaoh's oldest son would someday be heralded a god [just like his dad]. However, Yahweh is the only God.
So, Pharaoh let the Israelite people go. The Passover has been celebrated ever since. This was the redemption of the Jewish people and God reminded them to never ever forget what HE did for them.
So, fast forward to Jesus. Jesus is celebrating Passover with his disciples when he changes the Passover rituals. He said the unleavened bread represented his body and the cup represented his body broken. He is letting them know that the redemption they celebrate through the slaughter of a Passover Lamb is done. He is now the once-for-all Passover Lamb. 1 Corinthians 5:7 says "For Christ, our Passover lamb, has been sacrificed." It is that Lamb that took our sins away (Jn 1:29). He also made a similar statement commanding us "This do in remembrance of me".
So, we still remember our redeemer, who redeems us from our slavery to sin every time we take communion.