Thomas Aquinas on Mt 16:18

Here’s a clear, accurate summary of Thomas Aquinas’ teaching on Matthew 16:18, grounded directly in the sources surfaced by the search results.

Thomas Aquinas on Matthew 16:18

Aquinas does not give a single, rigid interpretation of “the rock.” Instead, he preserves multiple legitimate readings drawn from earlier Fathers, especially Augustine. His approach is both/and, not either/or.

1. Aquinas presents several valid interpretations

He cites Augustine’s Retractions to show that the passage can be understood in more than one orthodox way:

• The rock is Christ Himself. Aquinas quotes 1 Corinthians 10:4 (“the rock was Christ”) and 1 Corinthians 3:11 (“no other foundation can be laid”).
• The rock is Peter. Not by nature, but because Peter receives stability from Christ and confesses Christ.
• The rock is Peter’s confession of faith. The truth he proclaimed — “You are the Messiah, the Son of the living God.”

Aquinas does not force a single interpretation; he allows the Church to hold all three as harmonious.

2. Christ is the foundation in Himself

Aquinas is explicit: Christ alone is the foundation “in Himself.” Peter and the apostles are foundations only by participation, through the authority Christ delegates to them. He cites Ephesians 2:20 and Revelation 21:14 to show that the apostles are “foundations” only because Christ makes them so.

3. Peter is a foundation only insofar as he confesses Christ

Aquinas resolves the tension this way:

• Christ is the true Rock.
• Peter becomes a “rock” only because he receives from Christ the revelation and authority he confesses.
• Peter’s stability is derivative, not intrinsic.

This is why Aquinas says Peter is a foundation “insofar as he confesses Christ, and insofar as he is His vicar.”

4. The Church built on this rock cannot be conquered

Aquinas emphasizes that the “house” founded on this rock — whether understood as Christ, Peter, or Peter’s confession — cannot be destroyed, though it may be attacked. This echoes his commentary on Matthew 7:24–25.

In one concise summary

Aquinas teaches that Christ is the true Rock and foundation. Peter is a rock only by participation — because he confesses Christ and receives delegated authority. The “rock” of Matthew 16:18 can legitimately refer to Christ, to Peter, or to Peter’s confession, and the Church built on this foundation cannot be overcome.