Radak

Let us break their bands asunder: – They were saying: “Let us break the bands of Israel and their league (lit. binding) in which they have bound themselves and agreed to make David king.” For there had elapsed seven years in which Israel as a whole had not agreed about him to make him king, and now when they had all agreed about him the Philistines said “let us break their bands asunder.” And cast away their cords from us: – He repeats himself in different words, while the meaning is the same for such is the idiom of the language. And the “bands” and “cords” denote the strongest ropes, and are a figure for counsel and firm agreement.