Tafsir of As-Sajdah 32:18

This means: after the manifestation of the disparity between them, which is self-evident, it is impossible to imagine that the believer, whose virtuous attributes have been recounted, is like the transgressor, whose ugly and void states have been mentioned.

The origin of fisq (transgression) is 'exiting,' as in the phrase "the fruit fasaqat" (broke/exited) when it emerges from its peel. It was then used to mean exiting from obedience and the rulings of the Law in an absolute sense. Thus, it is more general than disbelief (kufr), though it is sometimes specifically used for it, as in His saying: "And whoever disbelieves after that, then those are the transgressors," and as it is here, due to its being contrasted with the believer—along with what you will hear subsequently, God willing.

{ They are not equal. }

This statement is made explicitly, while providing a denial to negate any resemblance whatsoever in the most eloquent and emphatic manner, for the sake of added emphasis and to build the subsequent detailed explanation upon it. The use of the plural in { They are not equal } takes into account the meaning of man (he who), just as the singular in the preceding part took into account its wording. It is also said that the pronoun refers to two, namely the believer and the disbeliever, and the dual form is represented here by the plural.