"To gently pat our shoulders" means that he would set their shoulders right to straighten the row. "Do not differ from each other" here means that they should stand shoulder to shoulder and ankle to ankle in a straight line. The reason is that disorder will have a spiritual effect and will create discord. The latter would eventually result in the domination of enmity. Thus, we learn from this Hadith that the Imam should stress on his followers the importance of setting their rows straight; and if his exhortation fails, he should go to them personally and set their lines in order. We also learn from this Hadith that men known for wisdom, knowledge and piety should stand in the first row and these should be followed by those who come next to them in these virtues.