Tafsir of Al-Kahf 18:108

(Abiding eternally therein): It is in the accusative case as a circumstantial qualifier (hal). Some consider it a prospective qualifier, but it has been established that it is a comparative circumstantial qualifier. What is considered in comparison is the time of the ruling, which is their existence in Paradise; since they are present within it, they are in a state of comparison with it, for there is no end to it—so reflect and be not heedless.

(They will not desire any change from it): As Ibn Isa and others have stated, it is a verbal noun, similar to al-‘awj (crookedness), al-sighar (smallness), and the ‘awd in the poet’s saying: "Her love has returned to me as a recurring return." That is, they will not seek a transformation from it, for it is inconceivable that anything could be dearer or more exalted to them than it, such that their souls would crave it or their eyes would look beyond it, even if their ranks vary. In sum, the intent behind the negation of seeking a change from it is that it is the most pleasant and highest of abodes.

Ibn Atiyyah said: It is as if it were a collective noun, the singular of which would be hawalah, but its remoteness is not hidden. Al-Zajjaj reported from some that it carries the meaning of heelah (stratagem/resource) in moving, but this is weak and contrived. It is permitted that the intent is to negate movement and transition, serving as a confirmation of eternity, for the lack of desire to move necessitates eternity; thus, it reinforces it. Or, it is as in the proverb: "And you will not see the lizard burrowing therein," meaning they will not move from it to seek anything else.

It is also said regarding the mode of confirmation: if they do not desire transition, they will not transition, because there is no compulsion in Paradise and there is no desire to depart from it. Thus, nothing remains but eternity, for there is no intermediary between them, as has been said. The clause is a circumstantial qualifier for the subject of "abiding" or for its pronoun therein, thus making it a nested circumstantial clause. In this, there is an indication that eternity does not cause them boredom.