שמואל ב, פרק ט״ו, פסוק ל״ג

During a desperate and difficult escape, a fleeing king is forced to turn away a deeply loyal friend who wishes to join him. David explains to Hushai that coming along on this harsh journey of wandering would only result in him becoming a heavy burden and a source of trouble [רד״ק].

The primary approach among commentators is that Hushai was an elderly man rather than a warrior. Because his physical strength had faded, his travel along the rugged roads would be slow and difficult, leaving him unable to offer meaningful help in a physical struggle [מצודת דוד, רלב״ג, ביאור שטיינזלץ, אברבנאל]. Furthermore, this physical limitation was compounded by David's own difficult reality. He was already accompanied by a large group of people who were a constant source of worry and grief for him. Adding yet another individual to this vulnerable group would only increase the logistical and emotional strain on the king [רד״ק, אברבנאל].

Rather than taking him into the wilderness, David assigns his trusted friend a crucial strategic mission. By returning to the city, Hushai would no longer be a burden on the road. Instead, he could use his wisdom and counsel to actively protect David from afar, positioning himself perfectly to sabotage and defeat the dangerous advice of Ahithophel [רד״ק, אברבנאל].