וַיִּשְׂמְח֤וּ הָעָם֙ עַל־הִֽתְנַדְּבָ֔ם כִּ֚י בְּלֵ֣ב שָׁלֵ֔ם הִֽתְנַדְּב֖וּ לַיהוָ֑ה וְגַם֙ דָּוִ֣יד הַמֶּ֔לֶךְ שָׂמַ֖ח שִׂמְחָ֥ה גְדוֹלָֽה׃ (פ)
百姓因自己甘心樂意的奉獻而歡喜，因為他們是誠心誠意地向永恆者奉獻；大衛王也大大地歡喜。
Rashi
for... wholeheartedly With one heart they gave, with the desire of their soul, and not with two hearts, for there is a person who gives against his will and not with an eager soul or because he is ashamed of others, and that is called two hearts, but all these gave with the desire of their soul.
Rashi
and King David also rejoiced a great rejoicing And lest you say that [he rejoiced] like them but no more, Scripture therefore states: “... and King David also rejoiced, etc.,” more than all of them, because he was the performer of the deed. A similar case (Jud. 5:5): “The mountains melted at the presence of the Lord; this was Sinai”: more than all of them, (Ex. 19:18): “... because the Lord had descended upon it in fire.”