Overall meaning : Beware of the day when He will gather you all for the Day of Gathering (Judgement Day)—that will be a Day of Loss and Gain (Loss for the unbelievers who will be cast into Hell, and gain for the believers who will be admitted into Paradise, with the unbelievers feeling they are disillusioned when they realise that by the believers will have taken their places in Paradise, which would have been theirs had they been true believers).
For those who believe in Allah and obey His commands, Allah will efface their bad deeds and admit them into Gardens underneath which rivers flow, where they will abide for ever. That is the greatest success.
As for those who disbelieve in Allah and deny His signs bearing witness to His power and oneness, they will be the dwellers if the Fire, where they will abide for ever—a terrible destination indeed!’