Even in moments of apparent peace, a hunted man can never truly rest. Although King Saul appears to have reconciled with David, a storm of deep fear continues to rage within David's heart. Despite God's promises and the miraculous ways he was saved in the past, David refuses to rely on miracles to keep him safe [אברבנאל]. He knows that supernatural interventions are not everyday occurrences, and he worries that his spiritual merits might have already been exhausted by the two previous times he was rescued [מלבי״ם, ביאור שטיינזלץ].
Paradoxically, David realizes that his own success, along with Saul's growing awareness that God is with him, only makes his situation more dangerous. Saul's worst fear that David will eventually take the throne has now been confirmed. Because of this, David knows the king's jealousy will only intensify, driving him to try even harder to end David's life [אברבנאל].
This heavy realization leads David to a grim conclusion: he is at risk of complete destruction [רד״ק, מצודת ציון]. He lives in constant dread that Saul will set an ambush and launch a surprise attack, ending his life in a single day before he has any chance to prepare or defend himself [רש״י, מצודת דוד]. Seeing no other way to survive, David decides his only remaining option is to flee to the land of the Philistines. This drastic move is designed to force Saul into abandoning the chase [רד״ק, מצודת ציון].
Escaping across enemy lines serves three clear strategic purposes. First, it will convince Saul that David is not secretly gathering an army within the country to stage a rebellion. Second, it will cause the king to finally give up his search within the borders of Israel. Finally, even if Saul decides to cross the border and pursue him, the Philistine king would step in to offer David his protection [מלבי״ם].
This journey to the Philistines stands in sharp contrast to David's previous experience. In the past, he fled to Achish, the king of Gath, alone and terrified, forced to act like a madman just to stay alive. Now, the circumstances are entirely different. He arrives as the leader of a six-hundred-man army, publicly known to be locked in a bitter, open conflict with Saul and the Israelites. Because of this new standing, David believes that Achish will welcome him warmly, eager to use him and his loyal men as allies in the ongoing war against Israel [אברבנאל].