Ephesians 6:15
And your feet shod with the preparation of the gospel of peace;
Cross-reference
Isaiah 52:7
Allusion
In Isaiah 52:7, feet bringing good news of peace and salvation are called beautiful — the direct OT source for this armor piece.
Romans 10:15
Citation
In Romans 10:15, Paul quotes Isaiah 52:7 about beautiful feet preaching good news — the same OT verse underlying Ephesians 6:15.
2 Corinthians 5:18–21
Parallel
In 2 Corinthians 5:18-21, the ministry of reconciliation is described — directly parallel to the gospel of peace that readies believers.
Exodus 12:11
Typology
In Exodus 12:11, Israelites eat Passover with sandals on, ready to leave Egypt — a type of the readiness for spiritual battle here.