When Saul took his sword and fell upon it (1 Samuel 31:4), it was the culmination of a long process of self destruction. It is hard to understand how a man anointed by God to be king of Israel could come to such an end, but it makes sense given that Saul was determined to keep David from inheriting the throne.
Saul made himself an enemy of God. In much the same way that Satan rebelled against God’s authority, Saul would not submit himself to God’s will and was a bad influence on everyone around him.
When Saul and his three sons were killed in battle, it says in 1 Samuel 31:7, “the men that were on the other side of the valley, and they that were on the other side Jordan, saw that the men of Israel fled, and that Saul and his sons were dead, they forsook the cities and fled; and the Philistines came and dwelt in them.” The word dwelt means that they took up residence there, the land became the Philistines possession.
As a result of their conquest, the Philistines became arrogant and gave tribute to their gods for the victory. This worst case scenario outcome probably caused more spiritual damage than anything else and was a turning point for the nation of Israel. King Saul’s reign proved to the people that no man was qualified to be their savior. It was God and God alone that could deliver them from the hands of their enemies and he was not going to until they acknowledged his kingship and rule over the nation.