This refers to the source of the baptism of John. Alternate translation: "If we say, 'It was from heaven,'" (See: [[rc://en/ta/man/translate/figs-ellipsis]])
Here "heaven" refers to God. See how you translated this in [Mark 11:30](./30.md). Alternate translation: "From God" (See: [[rc://en/ta/man/translate/figs-metonymy]])