The Qur'an says it plainly: Qârûn was from the people of Mûsâ (peace be upon him).
According to Ibn 'Abbâs, cited by Ibn Kathîr, he was Mûsâ's cousin. The Qur'an itself does not say so.
Elsewhere, the Qur'an names him beside Pharaoh and Hâmân: Mûsâ was sent to all three.
He was one of Mûsâ's own people, yet he stood with the powerful. The danger came from within.
Indeed, Qârûn was from the people of Mûsâ, but he tyrannized them.
And We gave him of treasures whose keys would burden a band of strong men.
It is not the treasures that weigh, it is the keys. The keys alone were a burden for a group of strong men.
Early commentators describe these keys and what carried them. Ibn Kathîr cites several views and ends: Allah knows best.
And “he tyrannized them”: the wealth did not stay in his chests. It turned against his own people.
His people spoke to him. Ibn Kathîr says it was the righteous among them, to advise him sincerely.
“Do not exult. Indeed, Allah does not like the exultant.
Seek, through what Allah has given you, the home of the Hereafter, and do not forget your share of the world.
Do good as Allah has done good to you, and do not seek corruption in the land.”
Look at what they do not say. They never tell him to throw his wealth away.
For Ibn Kathîr, “your share” is the lawful food, clothing and home. Give each right its due.
What they ask of him is a direction: to use what he was given to reach the Hereafter, and to do good with it.
He said: “I was only given it because of knowledge I have.”
Ibn Kathîr gives two readings: “because of my skill”, or “because Allah knows that I deserve it”.
Either way, the same thing is missing: he does not see the Giver.
The Qur'an quotes the same sentence about man in general, and answers: “Rather, it is a trial” (39:49).
Did he not know that Allah had destroyed before him generations greater than him in power and in wealth?
He boasted of his knowledge. The Qur'an answers with history: others had more, and they are gone.
His treasures were so many that a band of strong men struggled with the keys alone.
His people gave him advice. What he answered cost him everything.
Qârûn had everything except one sentence: this is from my Lord.
Tonight, name three things you own and say over each: “This is from the bounty of my Lord” (27:40).