إلا تنفروا يعذبكم عذابا أليما ويستبدل قوما غيركم ولا تضروه شيئا والله (9:39) بالانجليزي

(9:39) If you will not march forth, Allah will inflict on you a painful chastisement, *40 and will substitute other people for you, *41 and you will in no way harm Him, for Allah has power over everything.

Tafseer Abu-al-A'la Maududi

Page 193 English Traditional

*40) A general rule of the Islamic conduct has been derived from "If you .... chastisement. " When the Muslims are commanded to go to Jihad by a public proclamation from their leader, it becomes an obligatory duty for those who are called upon to do Jihad, whether they belong to any particular group or region. So much so that the Faith of those who do not go for Jihad without a genuine excuse becomes doubtful. But even in cases where the Muslims are called upon to go forth for Jihad and there is no command for the compulsory enrolment of every able-bodied Muslim of a particular group or region, it is a religious duty (though not obligatory), and it shall be considered to have been performed even if only some Muslims go forth for it.
*41) That is, "Allah's work does not depend on you and will be accomplished only if you do it. It is Allah's grace and bounty that He is affording you the golden opportunity of serving the cause of His Way. Therefore if you miss this opportunity because of any foolish assumption, Allah will raise another people and bestow on them the opportunity and capability of doing His work, and you will be losers".