v 61-62 Jesus equates believing in His Real Presence in the Eucharist with believing in the Resurrection.  Both require faith.  If you can’t trust Jesus with his statements about the first, you will have a tough time believing the 2nd, since both go against our human logic.

v 68 Peter didn’t grasp all of what Jesus was saying about Eucharist, or His Resurrection, but he trusted Jesus.  That’s what He asks of us.

v 68 We can’t get the Real Presence outside of His Church!

v70-71 Apparently, Judas, first mentioned here in John’s gospel, was among those who didn’t believe that Jesus would be present in Eucharist.  This may have led to his betrayal of Jesus.