Now I have prepared with all my might for the house of my God the gold for the [things of] gold, and the silver for the [things of] silver, and the brass for the [things of] brass, the iron for the [things of] iron, and wood for the [things of] wood; onyx stones, and [stones] to be set, stones for inlaid work, and of various colors, and all manner of precious stones, and marble stones in abundance.
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?"