The reason for the Real Presence is simple. The New Covenant is all about grace; it’s about man’s need for God, for intimate communion with Him, and the sacraments acknowledge, in a structured, physical way, God’s will and provide a means to carry out that will in some most basic ways. So Baptism, the “sacrament of faith”, gains entrance to God’s kingdom in obedience to Christ’s command, as a first formal and public profession of our faith. The Eucharist, received at First Holy Communion, recognizes our continuous need for that direct relationship with God, ‘apart from whom we can do nothing’ (John 15:5), and the nurturing that takes place as He resides in us. This communion is what man’s justice consists of; we were made for it, and Adam broke it. And if we break communion with Him, by serious or grave sin-acts against love of God and/or neighbor, grace is lost; we’ve separated ourselves from God again, breaking the reconciliation that Jesus won for us-and so likewise we’re to cease partaking of the Eucharist, acknowledging in real time what has already transpired within. So now the sacrament of Reconciliation is available in order to restore that communion, whereupon we may resume partaking of the Host, living out physically what has likewise occurred spiritually within.
This gives definition and understanding to our faith, arguably even more critical during the majority of centuries when most believers were illiterate and this simple means of relating to God put it all in perspective. And this all works simply because it’s true. Baptism really effects regeneration, Jesus is really Present in the Eucharist. Forgiveness is really achieved in the Sacrament of Reconciliation/Confession. At least for those properly disposed, those who truly believe, who really want what God offers rather than practicing it all mechanically, admittedly a very human trap to fall into BTW, one which we need to guard against. Anyway, it’s all grace, the difference between the Old Covenant, where man is “under the Law”, and the New, where he is “under grace”. These sacraments are New Covenant theology in action, putting into practice the NC prophecy of Jer 31:33-34.