What is the interpretation of verses 84-90, along with the story of Dhul-Qarnayn?

The story of Dhul-Qarnayn, mentioned in Surat Al-Kahf, begins with Allah empowering him on Earth and granting him the means to reach the setting place of the sun, where he found it setting in a dark, turbid spring and a people living there. He was given the choice to either punish them or treat them kindly. He declared that he would punish the unjust, returning them to their Lord for a severe torment, while rewarding the righteous believer with Paradise and good treatment.

Then, he journeyed eastward until he reached the rising place of the sun, where he found a people who had no shelter from it, which confirms Allah's encompassment of all his movements. After that, he journeyed northward until he reached between the two mountains (saddain), where he found a people who could barely understand a word. He comprehended their complaint about Gog and Magog, who were corrupting the Earth. They offered him money to build a barrier for them, but Dhul-Qarnayn refused the money and asked for their assistance in building a strong barrier of iron blocks and molten copper to prevent Gog and Magog from crossing.

After completing the barrier, which Gog and Magog could neither scale nor pierce, Dhul-Qarnayn attributed this achievement to the mercy of his Lord, acknowledging Allah's favor upon him, unlike the arrogant. He indicated that the barrier would collapse and be leveled with the ground when the promise of his Lord comes, with the emergence of Gog and Magog.