Prophet and seer in David's reign
Gad is presented in the books of Samuel and Chronicles as a prophet closely associated with King David. In 2 Samuel 24:11 he is given the title 'the king's seer.' His ministry was that of conveying the word of God to the king at decisive moments, both in counsel and in correction.
After David ordered a census of Israel and afterward confessed his sin, God sent Gad to present David with a choice among three forms of punishment (2 Samuel 24:11-13; 1 Chronicles 21:9-13). When the ensuing plague had run its course, Gad instructed David to build an altar to the Lord on the threshing floor of Araunah the Jebusite (2 Samuel 24:18), a site that later tradition associated with the Temple. The parallel account in 1 Chronicles 21:18-19 links this instruction to the appearance of the angel of the Lord.