Tafsir of Al-Kahf 18:59

{And those towns, We destroyed them...}

He means the towns of the ancients, such as Thamud, the people of Lot, and others. He pointed to them so that they might take heed.

• {تلك} (Those): Is the subject (mubtada’).
• {القرى} (The towns): Is an adjective (sifah), because demonstrative pronouns are described by generic nouns.
• {أهلكناهم} (We destroyed them): Is the predicate (khabar).

It is also permissible for {تلك القرى} to be in the accusative case (nasb) due to an implied verb "We destroyed" (ahlakna), based on the condition of explanation. The meaning is: "And those [people of] the towns, We destroyed them."

{لما ظلموا} (When they did wrong): Like the wrongdoing of the people of Mecca.

{وجعلنا لمهلكهم موعدا} (And We appointed for their destruction a time): We set a known time for their destruction, which they would not delay, just as We set a time for the people of Mecca on the day of Badr.

• {المهلك} (Al-mahlak): Refers to the act of destruction or its time.
• It is read as {لِمَهْلِكهم} (with a fatha on the mim), and the lam can be read with a fatha or a kasra, meaning: for their destruction or the time of their destruction.
• {الموعد} (The appointment): Is a time or a verbal noun (masdar).

{And [mention] when Moses said to his servant, "I will not cease until I reach the junction of the two seas, or I will continue for a long period."}

{But when they reached the junction between them, they forgot their fish, and it took its course into the sea, slipping away.}

{So when they had passed beyond it, he said to his servant, "Bring us our morning meal. We have certainly suffered much fatigue from this journey of ours."}

{He said, "Did you see when we rested at the rock? Indeed, I forgot [to mention] the fish. And none made me forget it except Satan—that I should mention it. And it took its course into the sea, amazingly."}

{He said, "That is what we were seeking." So they returned, following their footsteps.}

{And they found a servant from among Our servants to whom We had given mercy from Us and had taught him from Us a [certain] knowledge.}