قَالُوا يَا ذَا الْقَرْنَيْنِ إِنَّ يَأْجُوجَ وَمَأْجُوجَ مُفْسِدُونَ فِي الْأَرْضِ فَهَلْ نَجْعَلُ لَكَ خَرْجًا عَلَىٰ أَن تَجْعَلَ بَيْنَنَا وَبَيْنَهُمْ سَدًّا ﴿٩٤﴾ قَالَ مَا مَكَّنِّي فِيهِ رَبِّي خَيْرٌ فَأَعِينُونِي بِقُوَّةٍ أَجْعَلْ بَيْنَكُمْ وَبَيْنَهُمْ رَدْمًا ﴿٩٥
These are the two versus from سورة الكهف ayat 94 and 95 depicting the story of Dhul-Qarnain. Dhul-Qarnain was tendered to build a "Wall سَدًّا" to seperate a nation from the evils of Gog-&-Magog. In return, Dhul-Qarnain offered them to build a "Barrier/Dam رَدْمًا" voluntarily...
Lessons:
1. Try and seperate yourself from the evil elements in your vicinity.
2. If you can't do it by yourself, or if more people than just yourself are being affected, consult one another and see if there is someone who can do it.
3. Be grateful with what Allah has blessed you with. Firstly, you have to acknowledg the things that are being entrusted onto you by Allah, and then thank him and be grateful and use them to his Will.
4. Use those blessings to benefit yourself and others. Allah has trusted us with so many things, and in return we have to serve him sometimes by serving his creations in his way and for his cause.
5. Working is in and part of our Deen. Working for money is part of our deen, but it also shows more appreciation for Allah's blessings if we sometimes work expecting no worldly returns, purely for the sake of Allah, if we don't need it.
6. If someone asks for some form of help, offer them the best help. For example, if someone asks you to build them a wall for protection, offer to build them a barrier or dam. There is more ajr, inshAllah.
7. If someone asks for something from you out of sincere concern for themselves and the Ummah, help them out to the best of your ability to ease their burdens, and make them feel more comfortable about the situation. For instance here, the reason for the wall being asked to be built was for the sake of protecting themselves from the evils and troubles brought forth by Gog and Magog [aka Ya'jooj and Ma'Jooj], which is a sincere reason. Therefore, the reaction of Dhul Qarnain was the best, and he genuinely did his best by giving them better than was asked and expected of him. I hope I communicated that point well enough.
8. [This may seem like a repeated point, but it's only because it's all interrelated, but it's separate] Dhul Qarnain, as we learned from that lecture, was a leader. He lead the entire world. I'm going to go ahead and assume he was already a leader during this particular incident, seeing as the people asked HIM to help. So, in that situation, he displayed superb leadership. The lesson: If you lead a people, take their best interests at heart, and do all in your power to help them and keep them safe. You are there to serve THEM, and not the other way around. Sure, you rule over them, but only as a central figure to settle differences and make key decisions and such. But in reality, a true leader, however powerful, will do what is best for the people, as opposed to doing what's best for himself and just serving his own greed and worldly desires. And he didn't accept their payments, because as a leader, he is only doing his duty by serving them, and since he was capable of doing the job without their money with what Allah had already provided him, he did it without taking more from the people.