Period of Revelation
It appears from the tone of the Sura that it belongs to that group of the Suras which were revealed during the last stage of the Makkan period. For instance
v. 13 ("The disbellevers warned their Messengers
'you shall have to return to our community or we will assuredly expel you from our land'") clearly indicates that the persecution of the Muslims was at its worst at the time of the revelation of this Sura
and the people of Makkah were bent on expelling the Believers from there like the disbelievers of the former Prophets. That is why in v. 14 they have been warned
We will destroy these evil doers
and the Believers have been comforted as were the believers before them
and after them settle you in the land
Likewise the stern warning contained in the concluding portion (vv. 43-52 also confirms that the Sura relates to the last stage of the Makkan Period.
Central Theme and Purpose
This Sura is an admonition and a warning to the disbelievers who were rejecting the Message of the Holy Prophet and devising cunning schemes to defeat his Mission. But warning
censure and reproach dominate admonition. This is because a good deal of admonition had already been made in the preceding Suras
but in spite of this their obduracy
persecution etc. had rather increased.