This Surah was revealed in Makkah during the period when persecution of the Muslims was at its peak and the disbelievers of Makkah were trying their utmost by tyranny and coercion to turn away the new converts from Islam.

Major Issue, Divine Law and Guidance:
Those who torture the believers will be given the punishment of conflagration on the Day of Judgement
He Who created you for the first time will bring you back to life again for accountability
This Surah warns the disbelievers of the evil consequences of persecution and tyranny and consoles the believers that if they remain firm and steadfast against tyranny and coercion, they will be rewarded for it, and Allah Himself will avenge their persecutors. In this connection, the story of the people of the ditch (Ashab al-Ukhdud), who had burnt the believers to death by casting them into pits full of fire is related. By means of this story the believers and the disbelievers have been taught a few lessons:

That just as the people of the ditch became worthy of Allah's curse and punishment, the chiefs of Makkah are also becoming worthy of it.
That just as the believers at that time had willingly accepted to sacrifice their lives by being burnt to death in the pits of fire instead of turning away from their faith, so also should the believers now endure every persecution and never give up faith.
That Allah, to Whom belongs the Kingdom of the earth and heavens, is Praiseworthy and is watching what the two groups are striving for.
Therefore, the disbelievers will not only be punished in Hell for their disbelief but, in addition to that, they also will suffer punishment by fire as a fit recompense for their tyranny and cruelty. The believers who are firm in their belief and do good deeds will go to paradise.