Why did Allah allow Satan to continue?

The issue of Allah creating Iblees, there was certain good which came out of it whether in the case of Adam (عَلَيْهِ السَّلاَم), as we’ve seen Adam’s (عَلَيْهِ السَّلاَم) situation already and the good which came out of it. Or the other good which comes out in the world as a result of human being’s disobeying God under the influence of Satan etcetera but turning back to God in repentance, that greater good outweighing the evil.

The question remains as to, why did God allow him to continue? Ok, he started this evil thing, evil ball rolling. Why allow him to continue? Because of the fact that the test of this life would continue until the last day of this world. So Allah chose to have Iblees around until the last day to be a constant source of that evil element to produce the good amongst human beings that was required of them until the last day of this world. And we find in Qur’an,

“See this one You have honored above me”, arrogantly he’s talking to God, “If you give me respite until the day of resurrection, I will surely seize and mislead all of his descendants except a few.”[1]

But Allah wanted that few to be guided, and that few would become guided in the struggle with those satanic forces. So Allah gave him that respite, gave him that period of time till the last day of the world to create that confusion amongst human beings and draw some of them from the path to sift out, it was a means of weeding out the good from the evil amongst human beings. It is like a sieve with grain and is used to separate the good from the bad. Similarly Satan has played the role of separating out evil elements amongst human beings from the truly good elements. That evil element, is not one confined to the initial evil period but will remain as a necessary element for identifying good, for sifting out the evil from the good until the last day of this world.

Reference:

[1] [Qur’an 17:62]