Yours, Yahweh, is the greatness, the power, the glory, the victory, and the majesty: for all that is in the heavens and in the earth is yours. Yours is the kingdom, Yahweh, and you are exalted as head above all.
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?"