Is there not a cause? - i. e., is not Saul's promise, and the insolence of Goliath, a sufficent cause for what I am about to do?

Is there not a cause? - הלוא דבר הוא halo dabar hu. I believe the meaning is what several of the versions express: I have spoken but a word. And should a man be made an offender for a word?

And David said, What have I now done? [Is there] not a (i) cause?
(i) For his father's sending was a just occasion, and also he felt himself inwardly moved by God's Spirit.

And David said, what have I now done?.... That is criminal and blameworthy; as if he should say, I have only expressed an indignation against this uncircumcised Philistine, and a concern for the glory of God, and the honour of the people of Israel:
is there not a cause? either for his coming to the camp, being sent by his father; or of his expressing himself with indignation at the Philistine's defiance of the armies of Israel. Some take the sense to be, that he had done nothing, he had not committed any fact; it was mere words what he had said, he had attempted nothing, and therefore there was no reason to bear so hard upon him; to this purpose is the Targum,"what have I done as yet? is it not a word "only" which I have spoken?''but the former sense seems best.

A cause - Of my thus speaking? Is this giant invincible? Is our God unable to oppose him, and subdue him? However David is not deterred from his undertaking, by the hard words of Eliab. They that undertake public services must not think it strange, if they be opposed by those from whom they had reason to expect assistance, but must humbly go on with their work, in the face, not only of their enemies threats, but of their friends slights, suspicions, and censures.