שמואל א, פרק י״ח, פסוק י׳

The day following the women's victory song, which praised David more than the king, brings a dark psychological and spiritual turn to the royal palace. The king sinks into a deep depression, and an evil spirit rests upon him [רד״ק, מצודת ציון], manifesting as a severe attack of gloom [ביאור שטיינזלץ]. This sudden shift is directly linked to the events of the previous day. Deeply affected by the public comparison between himself and his young commander, Saul realizes that David is the better man the prophet Samuel had spoken of. The evil spirit he experiences is the painful internalization of God's will and His decree to tear the kingdom away from him [אברבנאל].

To manage these attacks, a routine is established. Whenever this dark spirit overtakes the king, David plays his music, just as he has done day after day, in an effort to calm his troubled mind [מצודת דוד, ביאור שטיינזלץ].

While the music plays, Saul's behavior becomes highly erratic. The primary approach among commentators is that he falls into a state of madness, speaking absolute nonsense [רש״י, רד״ק, מצודת ציון]. This erratic speech shares a striking resemblance to prophecy, as both the prophet and the madman speak in riddles and hints that ordinary people cannot easily understand [רש״י, מצודת ציון]. In this state of diminished clarity, Saul acts almost like a fortune teller, vocalizing a dark vision of his own future and predicting that David will take his crown [מלבי״ם, ביאור שטיינזלץ].

However, a different perspective completely rejects the idea that the king loses his mind. Instead, Saul sinks into deep, consuming thoughts about the future. Isolating himself, he calculates his own downfall and privately prophesies to himself that David is destined to be his successor. Consumed by these thoughts and gripping his spear like a warrior in battle, a deep-seated fear of losing his throne drives him to a deadly conclusion. He resolves to kill David [אברבנאל, ביאור שטיינזלץ]. It is this very obsession that invites the evil spirit, ultimately leading to his first attempt to strike David down [מלבי״ם].