The commandment God had given King Saul was very clear:
This is what the Lord of Heaven’s Armies has declared: I have decided to settle accounts with the nation of Amalek for opposing Israel when they came from Egypt. Now go and completely destroy the entire Amalekite nation—men, women, children, babies, cattle, sheep, goats, camels, and donkeys.”
1 Samuel 15:2-3 (NLT)
In fact, I do not believe it could have been any clearer. God had had enough of the Amalekites and now their account would be settled. It was over, done with and they would have no more descendants... nor would their livestock. Wow!
Saul did not obey God. He not only spared the life of the king but David later encounters Amalekites (1 Samuel 30) which would have been rather difficult if Saul had done what he said he had done. Instead of destroying all of them as God had commanded, apparently he may have only killed all of the soldiers or only the men, leaving the women and children. In addition to this, Saul failed to slaughter all of the animals. He only slaughtered those who were sick, injured or of poor quality and saved the best.
Here is what happened when Samuel confronts Saul:
When Samuel finally found him, Saul greeted him cheerfully. “May the Lord bless you,” he said. “I have carried out the Lord’s command!”
“Then what is all the bleating of sheep and goats and the lowing of cattle I hear?” Samuel demanded.
“It’s true that the army spared the best of the sheep, goats, and cattle,” Saul admitted. “But they are going to sacrifice them to the Lord your God. We have destroyed everything else.” 1 Samuel 15:13-15 (NLT)
If it wasn't such a serious matter, this encounter would be almost comical. Saul cheerfully greets Samuel and says he has carried out God's command. Meanwhile, the air is filled with the noise of sheep, goats and cattle. Hmm...
Saul appears to have squirmed a bit at this point but quickly shifts the blame upon his soldiers, they did it, not him and ... and... oh Saul suddenly has what he believes to be a stroke of genius. We're not going to actually keep the livestock, it is for God! Yeah, that's it! The livestock, which we should have destroyed, was merely allowed to live because we want to sacrifice it to God.
From our point of view, this might seem ludicrous. Just how stupid did Saul think Samuel was? Did he really think Samuel would believe him and even if he did, what about God? This is unbelievable and yet I wonder whether or not we have ever been guilty of doing the same. Have we ever attempted to justify our wrong actions by saying that it was okay because we were doing it for God?