G-d who created the universe resides in a piece of matzoh.
This statement suggests to me that you probably do not have much background or understanding of Catholic theology regarding the Eucharist, or else it is a purposeful attempt at creating a straw man argument, or simply mockery. That's not what we believe.
There are at least eight ways in which Catholics speak of Christ being somewhere present:
- He is present in the Church when it prays, since it is Christ who prays for us and in us, and to whom we pray as to our God. This is the sense in which we believe that where two or three are gathered together in Christ's name, he is there in the midst of them.
- He is present in the Church when it performs its works of mercy, not only because we do to Christ whatever good we do to his brethren, but also because it is Christ, performing these works through the Church, who continually assists the faithful with his divine love.
- He is present in the Church in its pilgrimage of struggle to reach the harbor of eternal life, since it is he who through faith dwells in our hearts and, through the Holy Spirit, whom he gives, pours his love into our hearts.
- He is present in the Church as it preaches his Gospel, since the Gospel which the Church proclaims is the word of God. It is preached in his name, by his authority, and with the assistance of his grace.
- He is present in the Church as it governs the people of God, since the sacred power inherent in the Mystical Body comes from him. As shepherd of shepherds he is present in the pastors who exercise the power conferred on them as successors of the apostles.
- He is present in the Church when it offers in his name the Sacrifice of the Mass, and he is present to the Church whenever it administers the sacraments.
Christ is present in all these ways because he is active in our regard, and his influence is experienced by those to whom he is present.
- He is present uniquely, however, in the Real Presence – a presence that is different from all the foregoing. It is the physical presence of Christ in our midst, no less truly than he is now present at the right hand of his Father. Consequently "this presence is called real – by which it is not intended to exclude all other types of presence as if they could not be 'real' too, but because it is presence in the fullest sense. It is a substantial presence of which Christ, the God-man, is wholly and entirely present." If we could make a graphic comparison, there is as much difference between Christ's presence in the Blessed Sacrament and his presence elsewhere on earth as there was between his presence among his disciples when he appeared to them on Easter Sunday night and his presence before and after the appearance.
If you are sincerely interested in understanding the history of doctrines on the Eucharist, both inside and outside of Catholicism, the best resource is undoubtably
Hidden Manna by James O'Connor.
At least this will give you an understanding of the Catholic Church's theology of the Eucharist on its on terms. If you want to engage in apologetics from the perspective of your own faith, which I'm sure you feel is important for you to do, knowing what Catholics really believe about the Eucharist will prevent you from just debating a straw man. You'll be able to critically engaging the Church on its own terms. And who knows, maybe you might decide the Catholic Church is right after all.
I don't need another book to explain it to me. I can use the Bible.
"... For the bread of God is he which cometh down from heaven, and giveth life unto the world. Then said they unto him, Lord, evermore give us this bread. And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst." John 6:33-35
Did O'Conner reference the "Catechism of the Catholic Church" in his explanation. It makes it quite clear that they believe the body and blood are truly present.