Translation, Commentary & Explanation of Chapter 18 Al-Kahfi.

Literal Translation of Verse 2.

As a straight path, to remind of severe punishments from HIM, and to give good news to those who believe, who do good deeds, that they will be handsomely rewarded.

Tafsir Jalalain.

As a straight path and guidance, to remind and to warn the unbelievers with the Quran, of severe punishments from HIM (ALLAH), and to give good news to those who believe, who do good deeds that they will be handsomely rewarded.
The word "qayyiman" meaning "straight path" is grammatically an explanation to the word "Al-Kitab" in verse 1 meaning "The Book".

Tafsir Muhammad Asad

This divine writ, which is unerringly straight is meant to warn the godless of a severe punishment from Him, and to give glad tidings to the believers who do good works, that they will get good rewards.
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Literal Translation of Verse 3.

They will be permanently in it forever.

Tafsir Jalaian.

That is they will be in Paradise forever and ever.

Tafsir Muhammad Asad.

They will dwell in a state of bliss beyond the count of time.
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