Tafsir of Al-Kahf 18:20

"Indeed, if they discover you..." is a justification for the preceding command and prohibition. The pronoun refers to "their people" (implied by "then send one of you"), or to the disbelievers indicated by the meaning, according to the choice of Abu Hayyan. It is also permissible that it refers to "one" (ahad), because it is general, so its pronoun may be pluralized, as in His saying: "And there is no one among you who could prevent Us from him."

"If they discover you" means: if they find you and learn of your location, or if they overcome you. The original meaning of "to appear/overcome" (zahara) is "to become upon the back of the earth." Since what is upon the earth is observed and within reach, it is used at times for "discovering" and at times for "overcoming and prevailing," and it is connected with the particle "ala" (upon). Zayd ibn Ali recited it as "yuzharu" (passive voice).

"They will stone you" — if you do not do what they want of you and remain steadfast upon what you are upon. The apparent meaning is killing by stoning with stones, which was a custom in ancient times for those who dissented in a grave matter, as it is more healing to hearts and people participate in it. Al-Hajjaj said: The meaning is stoning with speech, i.e., cursing, which is greater than killing for noble souls.

"Or return you to their religion" — meaning, make you revert to it and enter you into it while you are compelled. Returning to something in this sense does not necessitate having been involved in it previously. This has been narrated from Ibn Jubayr. It is also said that returning is used in its literal sense, which is the person's reverting to what he was upon, as the youths were upon the religion of their people initially. The preference for the word "in" (fi) over "to" (ila) was explained by some verifiers as indicating stability, which is more hateful. The possibility of stoning is presented before the possibility of returning because what is apparent from their state is steadfastness upon the religion, which leads to the former. The address pronoun in the four instances is for the sake of hyperbole in urging the one sent to do what is intended of him, and the others are for the sake of emphasizing the advice, for the purity of sincere counsel is more conducive to acceptance, and a person's concern for his own affair is greater and more abundant.

"And you will never succeed if you do" — meaning, if you enter into it in reality, even by compulsion and coercion, you will never attain good, neither in this world nor in the Hereafter. The logical connection based on this is that coercion into disbelief might be a cause for Satan to entice one into finding it pleasing and persisting in it. From what has been mentioned, the objection is invalidated that expressing disbelief under compulsion while concealing faith is pardoned in all eras, so how could the lack of success ever be predicated upon it? There is no need to claim that expressing disbelief was absolutely impermissible for them, nor is there a need to interpret "return you to their religion" as "inclining you towards it through compulsion or otherwise." So reflect upon this.