Albert Barnes Commentary Psalms 40:15

"Let them be desolate by reason of their shame That say unto me, Aha, aha." — Psalms 40:15 (ASV)

Let them be desolate - The word used here means to be astonished or amazed; then, to be laid waste, or made desolate. As used here, it refers to their purposes, and the wish or prayer is that they might be wholly unsuccessful, or that in respect to success they might be like a waste and desolate field where nothing grows.

For a reward - The word used here—עקב ‛êqeb—means the end, the last of anything; then, the recompense, reward, wages, as being the end, the result, or issue of a certain course of conduct. That is, in this case, the desolation prayed for would be a proper recompense for their purpose, or for what they said. “Of their shame.” Of their shameful act or purpose; their act as deserving of ignominy.

That say to me, Aha, aha - That use language of reproach and contempt. This is a term of exultation over another; a word of rejoicing at the calamities that come upon another; an act of joy over a fallen enemy (Ezekiel 25:3); see the note on Psalms 35:21 and the note on Psalms 35:25. As understood of the Messiah, this would refer to the taunts and reproaches of his enemies; the exultation which they manifested when they had him in their power—when they felt secure that their troubles concerning him were at an end, or that they would be troubled with him no more.

By putting him to death, they supposed that they might feel safe from further trouble from him. For this act, this note of exultation and joy on the part of the Jewish rulers, and of the people as stimulated by those rulers, the desolation that came upon them (the utter ruin of their temple, their city, and their nation) was an appropriate reward.

That desolation did not go beyond their desert for their treatment of the Messiah—as the ruin of the sinner in the future world will not go beyond his desert for having rejected the same Messiah as his Savior.