But Saul and the people spared Agag and the best of the sheep and of the oxen and of the fattened calves and the lambs, and all that was good, and would not utterly destroy them. All that was despised and worthless they devoted to destruction.
1 Samuel 15:9 ESV

When God requires something of man, it's important to give it in the way in which God specifies, not how we would rather do it. The means of righteousness are an integral part of the end.