From the beginning of Surah Al-Qasas to this point, the story of Sayyidna Musa (علیہ السلام) with the Pharaoh and his people was narrated. From here onward another story about his is being related which is about Qarun, who belonged to his own fraternity. This story has an affinity with the previous verses in that it was said in an earlier verse that the wealth you are given in this world is temporary, and it is not wise to get involved in its love. وَمَا أُوتِيتُم مِّن شَيْءٍ فَمَتَاعُ الْحَيَاةِ الدُّنْيَا (And whatever thing you are given is the enjoyment of the worldly life - 28:60). Now in the story of Qarun it is described that he forgot this caution after having received the wealth and got so much intoxicated by it that he displayed ingratitude and rejected to fulfill his obligations toward Allah Ta’ ala with regard to bounties he had received from Him. As a consequence of that, he was sunk in the ground along with his treasure.
Qarun is a non-Arabic word, perhaps from Hebrew. It is stated in the Qur'an itself that he belonged to the fraternity of Sayyidna Musa (علیہ السلام) ، Bani Isra'il. As for his actual relationship with Musa (علیہ السلام) ، there are different versions. In a narration of Sayyidna Ibn ` Abbas ؓ he is mentioned as a cousin of Sayyidna Musa (علیہ السلام) . There are some other versions also beside this. (Qurtubi and Ruh).
A narration of Muhammad Ibn Ishaq, reproduced in Ruh ul-Ma’ ani, has observed that Qarun remembered Torah more than any other Isra'ili, but turned out to be a hypocrite like Samiri. The cause of his hypocrisy was his misplaced love and greed for worldly wealth and status. Leadership of the entire Bani Isra’ il was conferred on Sayyidna Musa (علیہ السلام) and his brother, Sayyidna Harun (علیہ السلام) ، who was his assistant and partner in prophethood. Hence, Qarun got jealous that after all he was also a cousin, but why did he not have a share in the leadership. So, he made a complaint to that effect before Sayyidna Musa (علیہ السلام) . He replied that it was all from Allah Ta’ ala, and he had no power in this matter. But Qarun was not convinced on this reply and developed jealousy against Sayyidna Musa (علیہ السلام) .
فَبَغَىٰ عَلَيْهِمْ (Then he rebelled against them - 28:76). There are quite a few meanings of the word بَغَىٰ Bagha. The more popular meaning is to commit cruelty. It is possible to take this word in this meaning here. Thus the meaning of the sentence would be that having got intoxicated by his wealth, he started perpetrating cruelty on people. Yahya Ibn Sallam and Said Ibn Al-Musayyab have stated that Qarun was a wealthy man, and was appointed by the Pharaoh to keep vigilance on Bani Isra'il. Taking advantage of this position, he started harassing Bani Isra'il. (Qurtubi)
The other meaning of Bagha is conceit or arrogance. Many a commentators have adopted this meaning here. Hence, the meaning of the verse would be that having got intoxicated by his wealth, he became conceited and looked down upon Bani Isra'il.
وَآتَيْنَاهُ مِنَ الْكُنُوزِ (And We had given to then such treasures – 28 – 76. Kunuz کَنُوز is the plural of کَنز (Kanz), which means buried treasure. In the commonly used religious sense Kanz is that treasure on which zakah is not paid. Sayyidna 'Ata' ؓ has narrated that he got hold of a magnificent buried treasure of Sayyidna Yusuf (علیہ السلام) . (Ruh)
لَتَنُوءُ بِالْعُصْبَةِ (would weigh too heavy for a strong group - 28:76). The word نَاَء (Na’ a) means to bend down with weight, and عُصْبَةِ 'Usbah' means a group. The meaning of the sentence is that his treasures were so many and their keys were in such large number, that if a group of strong people would try to lift them, they would bend down under their weight. Normally the keys of the locks are light, but because of their large number, their weight had multiplied so much that it was not possible even for a group of strong persons to lift them all. (Ruh)
لَا تَفْرَحْ (Do not exult - 28:76). Literal meaning of the word فَرَح (Farah) is the happiness one gets as a result of an instant pleasure. Many a Qur'anic verses have declared Farah as contemptible, as in this very verse also إِنَّ اللَّـهَ لَا يُحِبُّ الْفَرِحِينَ (Allah does not like the exultant - 28:76). In another verse it is said لَا تَفْرَحُوا بِمَا آتَاكُمْ (nor rejoice in what has come to you - 57:23). Yet another verse says فَرِحُوا بِالْحَيَاةِ الدُّنْيَا (And they are happy with the worldly life - 13:26). But in some verses Farah is allowed, rather in a way it is declared as desirable. For example in verses, يَوْمَئِذٍ يَفْرَحُ الْمُؤْمِنُونَ (And on that day the believers will rejoice - 30:4) and فَبِذَٰلِكَ فَلْيَفْرَحُوا (with these they should rejoice - 10:58). All these verses put together give us the guideline that Farah is contemptible and is not allowed when it reaches the level of arrogance and boasting. Thus one gets to a point where he regards the attainment of pleasure as his own personal achievement, and not a gift and favour from Allah Ta’ ala. But if the happiness and pleasure does not get to that position, then it is not disallowed; rather in a way it is desirable. In such a situation happiness would be to express the gratitude to Allah Ta’ ala.