During times of illness or severe weakness, the most painful blow often comes not from an enemy, but from a trusted confidant. It is a sad but common human reality that during a crisis, those who appeared to be deeply loving friends can suddenly turn hostile [רד״ק]. This betrayal is carried out by someone who actively presented himself as a devoted companion [מאירי]. The bond was so close that the sufferer trusted this individual completely and even provided for his financial support [אבן עזרא, מצודת דוד, ביאור שטיינזלץ].
Historically, this deep breach of trust is reflected in the relationship between King David and his military commander, Joab. David placed his absolute confidence in Joab by sending him a secret letter regarding Uriah. However, Joab betrayed this trust by sharing the letter with others, leading to David's public humiliation and the desecration of God's name [אלשיך]. Another perspective views the betrayer as a highly trusted royal servant whose specific duty was to taste the king's food to protect him from poison. In a shocking twist, despite the immense trust placed in him and the personal risk involved in tasting the food first, this very servant joined a conspiracy to poison the king [מלבי״ם].
The nature of this betrayal takes several forms. The primary approach among commentators is that it involves a hidden ambush, where the once-trusted friend secretly sets a trap for the vulnerable individual. Alternatively, the betrayal is understood through a striking image of physical trampling and arrogance. The traitor symbolically raises his foot to step on and crush the weakened sufferer [רד״ק, מאירי, ביאור שטיינזלץ]. This arrogance might also be shown simply by the friend refusing to visit the sick person in his time of need [רד״ק, אבן עזרא].
In the context of Joab's actions, his betrayal caused David to be trampled even further by his enemies. From another angle, the act of raising a foot represents an ultimate outcome or result; the final consequence of Joab revealing the king's secret was far more devastating than any rumors that had circulated previously [אלשיך]. Ultimately, this profound shock is compared to a person leaning heavily on a trusted friend for physical support, only to have that same friend suddenly draw a weapon to strike him down [תורה תמימה].