Matthew Poole and continuators on 2 Samuel 21:2

2 And the king called the Gibeonites, and said unto them, (now the Gibeonites were not of the children of Israel, but of the remnant of the Amorites, and the children of Israel had sworn unto them: and Saul sought to slay them , in his zeal to the children of Israel and Judah).

i. e. He fought occasions and pretences how he might cut them off with some colour of Law or Justice, diligently searching out and aggravating their faults, and punishing them worse than they deserved; oppressing them with excessive labours, and openly killing some of them, and intending by degrees to wear them out.

e Conceiving, or rather, pretending that it was not for the honour, nor comfort, nor advantage of Gods people, to nourish any of that viperous brood in their Bosoms; and that howsoever Ioshua and the Princes which then were, had by their fraud been drawn into an Oath to preserve them, Iosh. 9. 15. yet in truth that Oath was contrary to Gods command, Exod. 23. 32. Deut. 7. 2. and therefore (as he thought) not to be observed. This was his pretence: but how little Zeal he had for God, or for the publick good of his people, is evident by the whole course of his life: and therefore it is more than probable he had some particular motive or design in the case: either, because some of them had highly provoked him, for whose sake he would be revenged of the whole race: or, because they being cut off, their Estates might be forfeited to the Crown: or, for some other reason now unknown.

Marginal references: Josh. 9. 3, 16, 17.