In today's Gospel reading from John 6, Jesus says (verse 56): "Whoever eats My flesh and drinks My Blood, remans in me and I in him." To remain in each other is to be one. (If A < B and B < A, then A = B. A mathematical certainty.) It is clear to me that if you truly believe that the Holy Eucharist is the true body and blood of Christ and partake of it, then you and he become one. Union with God is achieved!