Charles Ellicott Commentary 1 Samuel 17:29

"And David said, What have I now done? Is there not a cause?" — 1 Samuel 17:29 (ASV)

Is there not a cause? —David answers his jealous and overbearing elder brother with all gentleness and forbearance, but he does not cease to make his inquiries of the soldiers about the giant, nor does he refrain from loudly expressing his astonishment that such a public insult to the God of Israel was being allowed to continue for so many days. The Hebrew here would be more literally translated, “Is it not a word?” or “It was only a word,” thus seeking to lessen his elder brother’s anger. “What have I done? It was only a mere word. I was only speaking with holy anger about this impious challenge of the Philistine; nothing more.” The ancient versions understand this clause in this way.

If we take the rendering of the Authorized Version, then the meaning is quite clear. “You seem bitterly displeased with my zeal in this matter, but surely, is there not a good cause for my passionate emotion here—such an insult to our God?”