I don’t think I will be able to understand it. Thank you for trying.
I read some of what Thomas Aquinas wrote on it today and I don’t think I can grasp it. I am a scientific person and I don’t think I can make my brain work in a way that can understand it. The physical substance remains unchanged, yet something which I can’t put my finger on does change. This change is not physical, but it isn’t merely spiritual or merely the meaning of the elements.
I think to answer the question of the post would be mostly because I can’t even understand it. I don’t know if all 3000 of the new Christians in Acts 2 suddenly comprehended this idea after a short sermon before becoming (non-separated) Christians, and today we just struggle with it. Or maybe understanding it isn’t necessary to be a Christian and understand what Communion is actually all about - which is remembering Jesus’ sacrifice to provide salvation for man.
It is a mystery of faith. The central mystery of Catholic faith.
Mystery in theological terms means, God has revealed it to us, but we cannot fully grasp what God has revealed. including via science or philosophy. We never fully grasp it. Aquinas used the tool of philosophy, towards grasping what God has revealed, but it can only go so far.
The Christians in Acts were no different. We accept by faith, the mysteries that God has revealed. We continue to seek deeper understanding, for a lifetime.
I am a convert to Christianity. There wasn’t a sermon where I suddenly believed in the Real Presence. It was during Lent, before my baptism. I spent a lot of time in prayer before the Blessed Sacrament, thinking it was an awesome thing what God had revealed, but not sure that it wasn’t just people believing for the sake of believing. Like belief in God itself, as I came from atheism, and thought at one time that faith was believing, just because.
Faith itself, in my experience is no less a mystery of God, and is miraculous. 3000 converts is a miraculous event!
Prayer, is where we participate in the life of the Holy Trinity. I recommend you pray.