Surah 61. As-Saff, Ayah 4

I.e., in unison, with their deeds corresponding to their assertions of faith. This moral necessity is further illustrated - by its opposite - in the subsequent reference to Moses and the recalcitrant among his followers.

A battle array, in which a large number of men stand, march, or hold together against assault as if they were a solid wall, is a striking example of order, discipline, cohesion, and courage. "A solid cemented structure" is even a better simile than the usual "solid wall" as the "structure" or building implies a more diversified organisation held together in unity and strength, each part contributing strength in its own way, and the whole held together not like a mass but like a living organism. Cf. also xxxvii. I and n. 4031.