It is not wrong to fear when face to face with danger, but it is wrong to succumb to fear. Strong and courageous men are often afraid, but in spite of their fears they go forward to do resolute deeds.
Seek the Lord.
Jehoshaphat had for years been building up the strength of his nation by equipping armies and fortifying cities (ch. 17:12-19). But at this time of crisis he placed his trust, not in men, but in God.