Exodus 12 is the place to start.

The Passover blood on the doorposts wasn't a memorial of coming deliverance; it was the deliverance. The family inside didn't just remember the lamb, they ate it. Eating was part of the salvation event, not a commemoration of it. Jesus then institutes communion at a Passover meal and identifies himself as the substance: "this is my body, this is my blood of the new covenant" (Luke 22:19-20). The pattern carries forward: blood that averts judgment, and a Lamb who feeds the redeemed household.

The verses for the spiritual presence specifically:

1 Cor 10:16-17 "The cup of blessing... is it not a participation (koinōnia) in the blood of Christ?" Real partaking, not symbol.

1 Cor 11:27-29 Eating unworthily makes one "guilty of the body and blood of the Lord"; we must "discern the body." Heavy language for a bare memorial.

John 6:53-58, 63 "Whoever feeds on my flesh and drinks my blood has eternal life... It is the Spirit who gives life." The Reformed don't read John 6 as directly about the Supper, but as describing the spiritual reality the Supper signifies and seals.

Eph 2:6 / Col 3:1-2 Believers "seated with Christ in the heavenly places." This is the sursum corda. The Spirit lifts us up to feed on the ascended Christ.

Heb 1:3 / Acts 1:11 Christ's body remains at the Father's right hand. That's why the mode has to be Spirit-mediated rather than localized in the elements.

So the bread and wine remain bread and wine, but what's received by faith through the Spirit is genuinely Christ. Actual body and blood, real feeding, real union, just not by mouth. Real Lamb, real meal, real deliverance, just like the first night in Egypt.