This is an idiom that means he had disobeyed the commandment. Alternate translation: "I have disobeyed what Yahweh commanded" (See: [[rc://en/ta/man/translate/figs-idiom]])
Here "voice" refers to what the soldiers asked Saul to do. Alternate translation: "did what they asked" (See: [[rc://en/ta/man/translate/figs-metonymy]])