1 Samuel 14 records the second of Saul’s three falls: He sins when he sacrifices impetuously without waiting for Samuel (ch. 13), when he attacks Jonathan for eating during a battle (ch. 14), when he refuses to carry out the ban against the Amalekites (ch. 15).
Chapter 14 is also about Jonathan’s heroism. Alone with his armor bearer, he attacks the Philistine camp, sparks a panic, and enables Israel to win the battle. Saul’s response to this heroism is to propose to execute his son. Later, he will do the same with the hero David: David defeats Goliath in single combat, sparks an Israelite victory, wins the praise of the people, but Saul tries to kill him. The parallel is even stronger, since by the time Saul tries to kill David, David is Saul’s son-in-law.
The other moment of foreshadowing occurs in verse 21: “the Hebrews who were with the Philistines previously, who went up with them all around in the camp, even they also turned to be with the Israelites who were with Saul and Jonathan.” Apparently, some in Israel thought choosing the Philistines was choosing the winning side. When the discovered otherwise, they switched sides.
No wonder the Philistine lords are later suspicious that David is accompanying them out to battle against Saul (1 Samuel 29). They know what it’s like to have an Israelite fifth column in their midst, and they want to avoid another defeat.