Peter is affirming the divine and human authorship of the Bible.1 David may have written the psalms (or they were composed under his leadership), but their content is nothing less than the words of God the Holy Spirit. Peter will affirm the same truth in his letter (2 Peter 1:20–21).
16 “Brothers, the Scripture had to be fulfilled, which the Holy Spirit spoke beforehand by the mouth of David concerning Judas, who became a guide to those who arrested Jesus.