Tafsir of Al-Kahf 18:57

{By the signs of His Lord} Meaning the Qur’an. For this reason, the pronoun returned to it in the masculine form in His saying: {that they might understand it}.

{Then he turned away from them} He did not take heed when reminded, nor did he contemplate.

{And forgot} The consequence of {what his hands have put forth} of disbelief and sins, neither thinking about them nor considering that both the evildoer and the doer of good must inevitably receive their recompense.

Then He explains their turning away and their forgetting by stating that their hearts have been sealed. He uses the plural after the singular, carrying the meaning of man (whoever) in both its literal form and its intended meaning.

{So they will never be guided} There will be no guidance from them at all; it is as if it is impossible for them due to their extreme obstinacy.

{Ever} Throughout the entire duration of their accountability.

{If} This is a conditional particle and a response. It indicates the negation of their being guided to the Messenger’s call, in the sense that they made what should have been a cause for the existence of guidance into a cause for its negation. It also serves as a response to the Messenger, assuming he said: "Why do I not call them, out of my eagerness for their Islam?" It was said to him: "Even if you call them to guidance, they will never be guided."

{And your Lord is the Forgiving, Full of Mercy. If He were to impose blame upon them for what they earned, He would have hastened the punishment for them. But for them is an appointment from which they will find no refuge.}