Jāshat means surged or became agitated, with al-nafs as the subject. Khāla is a verb of supposition; khālahu muṣāban portrays the imagined calamity in which he sees himself.
Marṣad relates to watching, ambush, or a place where an attacker might wait. Wa-law amsā adds a concessive alternative: even away from an expected ambush route, dread can remain. The verse characterizes the desert journey as a psychological test.