The decision of Ahab and Jehoshaphat to march into battle together unfolds despite a severe warning of disaster delivered just moments prior. Their choice to advance can be understood by examining the balance of prophetic voices at the time [ביאור שטיינזלץ].
On one side stood a single prophet who predicted the fall of Ahab and the scattering of the people. Against him stood an entire group of prophets who confidently promised military success. Ahab had already undermined the lone prophet by claiming he only ever predicted negative outcomes, which successfully weakened the impact of his warning. Furthermore, because the dire prophecy did not include an explicit command forbidding them from fighting, Jehoshaphat was convinced of his path. He concluded that the proper course of action was to follow the majority opinion and proceed with the war.