The one who is afraid of the dangers that accompany war, whose anxiety overwhelms him, is sent home, lest his faintheartedness affect those around him. The Tchortkover Rebbe, z.l., was once asked by one of his chassidim which shul he should attend. It seems that his community had two synagogues; one was a large community shul, while the other was a small shtiebel frequented primarily by chassidim. The Rebbe responded that whichever shul had a member who prayed with a broken heart; that is the shul in which he should daven.
He supported his answer with the above pasuk. We derive from the pasuk that one person with a faint heart, who is devastated by his fear of battle, is sent home because of his negative effect on those around him. Certainly then if there is a shul member who is heart-broken, his effect will be all-encompassing.