David the king said to all the assembly, Solomon my son, whom alone God has chosen, is yet young and tender, and the work is great; for the palace is not for man, but for Yahweh God.
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?"