At the critical moment before facing his giant opponent, David dresses in the royal battle armor of King Saul. However, he quickly realizes that a conventional approach to this battle will not work, and he must rely entirely on his own identity and faith. Commentators debate his initial reaction to the heavy military gear. The primary approach suggests that David genuinely wanted to wear the armor and even attempted to walk in it [מצודת ציון, ביאור שטיינזלץ]. He fully intended to use the weapons but found them physically impractical [מצודת דוד, אברבנאל]. He only changed his mind upon realizing that he was completely unaccustomed to the weight and movement required, having never tested such equipment before [רד״ק, מצודת דוד, ביאור שטיינזלץ]. Conversely, another perspective argues that David never wanted to wear the armor in the first place, actively refusing to even try walking in it [רש״י, רד״ק].
Beyond the physical lack of experience, David had profound spiritual and psychological reasons for shedding the royal gear. On a spiritual level, he understood that fighting with standard weapons would make any triumph appear to be a natural military success. By rejecting the armor, David ensured that his impending victory would be recognized purely as a miracle, proving that salvation comes directly from God [רש״י, רד״ק].
On a psychological level, a hidden drama unfolded between the young shepherd and the king. Saul was famously tall, standing head and shoulders above everyone else, yet his massive armor miraculously adjusted to fit David perfectly. When Saul saw this supernatural fit, he grew pale with jealousy. Noticing the king's sudden distress, David quickly offered a diplomatic excuse. He claimed he could not wear the garments simply because he was not used to them, choosing to remove the armor entirely to protect Saul's dignity and ease his mind [אברבנאל].
As for King Saul, his willingness to send an inexperienced boy to the front lines stemmed from a deep trust in God's providence, paired with calculated military strategy. If David were to win through God's mercy, it would bring immense joy and victory to Israel. However, if David were to fall, the Israelites could easily reject Goliath's harsh terms of surrender. They could argue that the defeated challenger was merely an unauthorized youth, and his personal loss could not legally bind the entire national army [אברבנאל].