Commentary
Two behavior models of human beings appear in the cited verses side by side. As for those who elect to go for the readily available benefits out of their life in this world, and the punishment that comes in its wake, the words used were: مَّن كَانَ يُرِيدُ الْعَاجِلَةَ (Whoever opts for the immediate life herein - 18). These words signify continuity and permanence meaning that this punishment of Hell will materialize only when one's actions are all the time motivated by material interests only, having practically no concern for the Hereafter. And as for 'those who desire to have the Here-after and its rewards,' the words used were: أَرَادَ الْآخِرَةَ ۔ The sense is that as soon as a true believer were to form an intention to have the reward of the Hereafter in whatever he proposes to do, that deed of his shall stand accepted - irrespective of any corruptive element having entered into something else he was intending to do.
The first condition can only be that of a denier of the Hereafter, therefore, none of his deeds is acceptable. Then, the second condition is that of a true believer. A particular deed by him that issues forth with sincerity of intention, and is for the Hereafter - along with the presence of other conditions - shall be acceptable. And a deed even from the same person, a deed that has no sincerity, or where other conditions are missing, will not be acceptable.