What gift could be greater than the the gift of God Himself? The Eucharist is the Body, Blood, Soul, and Divinity of our Lord Jesus Christ and Jesus is the second person of the Trinity. He is fully God and fully man, not half God and half man. When we receive Communion we are partaking in the Divinity of Christ as well as his humanity because the two are inseparable. We consume Him and He consumes us. This is truth.
There are Catholics that do not believe in the Real Presence of Christ in the Eucharist. This brings to mind the Gospel of John when many walked away from Jesus because they could not accept his words. "How can this man give us his flesh to eat?" (Jn 6:52) Jesus let them walk away rather than compromise the truth of his words. "As a result of this, many of his disciples returned to their former way of life and no longer accompanied him." (Jn 6:66) What strikes me about this passage is "many of his disciples returned to their former way of life". In refusing to accept the truth they refused to be transformed and returned to their old ways. They didn't "walk with him" anymore.
We must walk with Jesus. He is "the way and the truth and the life" as he states in the Last Supper Discourses (see John chapter 14). Through the Eucharist we come to share in the life of Christ. Throughout the Old Testament and the New we see prefigurations of the Eucharist. The "showbread" , the "manna" in the desert, the priest Melchizedek who brought out the bread and wine. Even the place and manner of Jesus' birth points to the Eucharist. Bethlehem means "house of bread" and Jesus was born in a manger (a feeding trough). Where is the difficulty with understanding the truth about the Eucharist?
I find it interesting that there were twelve baskets of bread left over after Jesus miraculously fed the crowds (Jn. 6:13). Twelve is usually a symbol of the twelve tribes of Israel which signifies the Church. I connect this with the passages about the showbread in Leviticus 24: 5-9, another foreshadowing of the Eucharist. It points to Jesus feeding his church the "Bread of Life" in every age.
"How I hate this folly of not believing in the Eucharist, etc.! If the Gospel be true, if Jesus Christ be God, what difficulty is there?" Blaise Pascal