No matter what anyone says, this passage is clear. If Jesus had phrased this in the affirmative, "Whoever eats my flesh has life," then somebody could have challenged it by saying, "Those who don't eat it will also be saved." Some scoundrels also say, "Your teaching is correct, but ours is also correct. The Lord didn't mean to exclude other ways." They create many ways to receive eternal life, including praying to the saints, worshiping the Virgin Mary, or living in a monastery. But none of these ways can achieve eternal life. Christ excludes all other ways. They are all unacceptable.
Take a look at this from another angle. If I were to say, "Wittenberg beer quenches thirst. Annaberg beer also quenches thirst," then I don't exclude other beers. But it would be very different if I were to say, "If you don't drink Wittenberg beer, no other beer will quench your thirst." In the same way, Christ doesn't speak in the affirmative here. He excludes everything else when he says, "Unless you eat the flesh of the Son of Man and drink his blood, you have no life in you." If we despise his flesh, nothing else will prove helpful. I may call on Saint Mary or Saint Peter, but they cannot help me. It's out of the question. In a word, all other ways are rejected.
Life, grace, and salvation come to us by faith alone and not by good works. They become ours by believing and by eating and drinking the body and blood of Christ.
Grace, Freedom, Laughter!