Well there’s a lot that can be said with regards to those two topics. When I’m asked about the real presence of Christ in the Eucharist, a common place to turn is John 6. That entire chapter is centered around the Eucharist and the real presence.
If you’re familiar with the story in Exodus about the Jews’ flight from Egypt you can make the connection between the two events. Before the Jews fled Egypt they were commanded to take an unblemished lamb, kill it and then eat it. But they had to follow the commands to the letter, so they couldn’t eat a pig or a cow or anything else that symbolized the lamb, they had to eat the lamb.
So if Jesus is the new lamb. Which John the Baptist called Him when he saw Him coming, “behold the lamb of God” and since Jesus was celebrating that same Passover with his apostles; you’ll notice that when Jesus celebrates the Passover he doesn’t use a lamb, instead he takes the bread and tells his disciples “this is my body, which is given up for you, do this is in remembrance of me”.
And what exactly are they doing, they are instituting the new covenant and eating his body and drinking his blood. Just like Jesus told the crowd they would have to do in John 6.
Why would they have to do that, because when the Jews fled Egypt it wasn’t enough for them to just kill the lamb and spread its blood over the door post, they had to eat the lamb. So it isn’t enough that we merely remember Jesus’s death on the cross. For us, in order to have life just like the Jews, we have to eat the lamb or in this case the Eucharist, which is truly Jesus’ body and blood.