Now the acts of David the king, first and last, behold, they are written in the history of Samuel the seer, and in the history of Nathan the prophet, and in the history of Gad the seer,
So David is, has told of his own commitment and now he's challenging them for a commitment of giving to God. "This is what I have done. This is what I propose to do. Now who of you are willing to offer your service unto the Lord?"