2 Corinthians 10:13-16 parallels Paul's ambition to preach beyond current reach and not boast in work already done — identical to Romans 15:20.

2 Corinthians 10:14-16 explicitly states Paul's policy of not boasting in others' work and preaching in regions beyond — directly parallel to his ambition in Romans 15:20.

Isaiah 52:15 prophesies that those who have not heard will see and understand — directly quoted in Romans 15:21 as the scriptural basis for Paul's ambition.

In 1 Corinthians 3:10, Paul uses the same building metaphor—he laid a foundation, others build. This clarifies his ambition to avoid building on another's.

In 2 Corinthians 10:15, Paul says he does not boast in others' labors—the exact same principle as not building on another's foundation.

1 Corinthians 3:9-15 describes Paul laying a foundation and others building on it — complementing his avoidance of building on another's foundation.

In 1 Corinthians 4:15, Paul calls himself a father through the gospel—he was the first to preach. This echoes his desire to be the first to bring Christ to a region.

Isaiah 55:5 says nations that did not know you will come — reflecting Paul's mission to preach where Christ was not known.

In Colossians 1:29, Paul describes toiling and struggling for the gospel—the same effort behind his ambition to preach where Christ is not named.