Oh, man. There is a lot I can say about this.
I used to hold to Memorialism, but, the more I read Scripture the more I find that position problematic.
Here's a very brief summary of what won me over to an understanding of the Real Presence (a holy mystery, expressed in the Lutheran Church as the Sacramental Union):
- God throughout Scriptures often works through means. One of these means is a sacrificial meal. We see this idea in the eating of the fruit of the Tree of Life, and of the Tree of Knowledge of Good and Evil, in the Passover, and in the Eucharist.
- Consider who instituted the Eucharist. It's not made by man, but by God.
- Consider when it was instituted. Namely, on the night before Christ was betrayed. This makes the Eucharist a testament and the culmination of the Passover. That is, to the Church is given the true Passover meal, which is Christ's body and blood given to us.
- Consider the great promise attached to the Eucharist, and the stern warning against its abuse.
- If we look at early Church history, the idea of a mere memorial rite is entirely alien to how they understood the Eucharist.
- Grammatically, the sentence "This is my body" cannot be "This represents my body". I'm happy to explain this in more detail, but it's worth noting that at the Reformation, even the radical reformers championed by Zwingli admitted that grammatically speaking, it cannot be a symbol. Many different ideas were proposed, but in the end, they concluded that even if they cannot make it fit grammatically, they still opposed the orthodox understanding. This is why no (at least to my knowledge) Bible translation translates "is" to "symbolises".
- The argument that "This is my body" is comparable to "I Am the Door" etc, is false. The first reason for this is the grammatical reason mentioned above, and the other reason is that "I Am the Door", is not an expression, but literal. Christ is not saying that He is like a door, but that He truly IS the Way (that is, not "like the way"). So, in other words, they have different grammatical forms, and neither statements are symbolic.
- Perhaps the most important thing is that, when we talk about God's means of grace, namely, His Word, Baptism, and the Eucharist (we can also include Absolution), they are not things we do for God, but what God does for us. The Eucharist is simply the same Gospel message for our comfort, in a tangible form.