[ Abdullah Yusuf Ali ]
We sent aforetime our messengers with Clear Signs and sent down with them the Book and the Balance (of Right and Wrong), that men may stand forth in justice; and We sent down Iron, in which is (material for) mighty war, as well as many benefits for mankind, that Allah may test who it is that will help, Unseen, Him and His messengers: For Allah is Full of Strength, Exalted in Might (and able to enforce His Will).
[ Saheeh International ]
We have already sent Our messengers with clear evidences and sent down with them the Scripture and the balance that the people may maintain [their affairs] in justice. And We sent down iron, wherein is great military might and benefits for the people, and so that Allah may make evident those who support Him and His messengers unseen. Indeed, Allah is Powerful and Exalted in Might.
5313 Three things are mentioned as gifts of Allah. In concrete terms they are the Book, the Balance, and Iron, which stand as emblems of three things which hold society together, viz., Revelation, which commands Good and forbids Evil; Justice, which gives to each person his due; and the strong arm of the Law, which maintains sanctions for evildoers. For Balance, see also 42:17, and n. 4550.
5314 Sent down: anzala; in the sense of revealed to man the use of certain things, created in him the capacity of understanding and using them: Cf 39:6: "sent down for you eight head of cattle in pairs".
5315 Iron: the most useful metal known to man. Out of it is made steel, and from steel and iron are made implements of war, such as swords, spears, guns, etc., as well as instruments of peace, such as ploughshares, bricklayers' trowels, architects' and engineers' instruments, etc. Iron stands as the emblem of Strength, Power, Discipline, Law's sanctions, etc. Iron and steel industries have also been the foundation of the prosperity and power of modern manufacturing nations. (R).
5316 In 21:49, I have translated "in their most secret thoughts" for the more literal "unseen" (bi al ghayb). Perhaps the more literal "unseen" may do if understood in the adverbial sense as explained in 35:18, n. 3902. The sincere man will help the Cause, whether he is seen or brought under notice or not.
5317 To help Allah and His messengers is to help their Cause. It is to give men an opportunity of striving and fighting for His Cause and proving their true mettle, for thus is their spirit tested. As explained in the next line, Allah in Himself is Full of Strength, Exalted in Power, and Able to enforce His Will, and He has no need of others' assistance.
5318 Cf. 22:40 and n. 2818. "Strength" is specific; Power or Might is more abstract, the ability to enforce what is willed.