Overall meaning : The Almighty states that the believers should not go forth to war all together at the same time. Of every group of them, He teaches, a party only should go forth to fight so that the rest of Muslims may gain sound knowledge in Allah’s religion when they stay behind for this purpose, and so that those who stay behind to study their religion teach those who have gone forth to fight when they return to them, so that they, too, may be wary of the consequences of disobeying Allah and beware of His wrath and punishment.
Allah then enjoins the faithful to fight the unbelievers who live around them close to their territiry, ensure that the unbelievers should find them stern and formidable when they fight them, and to rest assured that Allah is with the righteous who do what he commands and avoid what he forbids.