What does 1 Samuel 15:9 mean?

But Saul and his men spared Agag and kept the best sheep, cattle, fattened calves, and lambs—anything that looked good. They destroyed only what was worthless or weak. 1 Samuel 15:9 - Modern Text Bible

(Instead of destroying everything, Saul and his army keep the best livestock and the king alive, disobeying God’s clear instructions.)