He waited seven days, the time set by Samuel; but Samuel did not come to Gilgal, and Saul's men began to scatter. So he said, "Bring me the burnt offering and the fellowship offerings." And Saul offered up the burnt offering (1 Sam 13:8-9).
Seeing the Philistines, as numerous as the sand on the seashore, being assembled to fight against Israel, all the troops with king Saul were quaking with fear, and many of those who followed him began to leave and scatter. So, Saul offered the burnt offering though he was not a priest. This offering was offered not to God, but to the people so that he could keep his men from leaving. It was done according to the idea of his mind. Just as he finished offering it, Samuel showed up, and said to him.
You acted foolishly. You have not kept the command the Lord your God gave you; if you had, he would have established your kingdom over Israel for all time. But now your kingdom will not endure (vv. 13-14); …
When a Christian walk according to the flesh—his own understanding and ideas, the fulfillment of God’s word stops. It is the same thing as eating from the tree of the knowledge of good and evil. The Bible says:
Trust in the Lord with all your heart
And lean not on your own understanding;
In all your ways acknowledge him,
And he will make your paths straight (Pro 3:5-6).
We have God’s presence all the time, but it is our responsibility to acknowledge him wherever we go. King Saul, when he was attacked by the Philistines, did not acknowledge the Lord, but leaned on his own understanding. Therefore, the word did not come to be fulfilled: his kingdom was not established.
You can compare this with the story of Jehoshaphat who was attacked by the allied forces of the Moabites and Ammonites—a vast army.
Alarmed, Jehoshaphat resolved to inquire of the Lord, and he proclaimed a fast for all Judah. The people of Judah came together to seek help from the Lord; indeed, they came from every town in Judah to seek him (2 Chr 20:3-4).
King Jehoshaphat put God first, not himself, or his own understanding. He stood before the temple of the Lord, and prayed:
O Lord, God of our fathers, are you not the God who is in heaven? You rule over all the kingdoms of the nations. … For we have no power to face this vast army that is attacking us. We do not know what to do, but our eyes are upon you (vv. 6-12).
This is what it means to trust the Lord with all your heart. So, the word of the Lord came to him:
Do not be afraid or discouraged because of this vast army. For the battle is not yours, but God's (v. 15).
Because he committed his way to the Lord, it was the Lord himself who did it by fulfilling his word. When you think you can still do it, fear comes and you fail with no fulfillment of his word. Jehoshaphat encouraged the people by saying:
Have faith in the Lord your God and you will be upheld;
Have faith in his prophets and you will be successful (v. 20).