In congregational prayer, worshippers stand toward one qiblah. Keeping rows straight visibly expresses shared order. The warning draws attention to the possibility that visible disorder may be accompanied by discord among hearts.
In صُفُوفَكُمْ, كُمْ addresses the congregation; بَيْنَ وُجُوهِكُمْ literally means “between your faces.” A good explanation preserves the original wording while clarifying its ethical significance. It should not claim that every disagreement among worshippers must be the direct fulfillment of this particular warning.