وَابْتَغِ فِيمَا آتَاكَ اللَّـهُ الدَّارَ الْآخِرَةَ ۖ وَلَا تَنسَ نَصِيبَكَ مِنَ الدُّنْيَا (And seek the (betterment of) the ultimate Abode with what Allah has given to you, and do not neglect your share from this world - 28:77). The Muslims advised Qarun that he should try to do as much good as possible for the Hereafter by utilizing the wealth Allah Ta’ ala had given him, and 'should not forget his share in the world'.
What is his 'share in this world'? Many commentators have explained that it refers to his life in this world and the deeds that may help him in the Hereafter which include charity and all other righteous deeds. Sayyidna Ibn ` Abbas ؓ has favoured this explanation. (Qurtubi) By adopting this explanation, the second sentence would be regarded as an emphasized repetition of the first sentence. The first sentence has directed that one should make use of all that has been gifted - the life, wealth, health, strength etc. - to collect that which would be of help in the Hereafter. In fact this portion of the worldly possessions is one's own, which may help him in the Hereafter; the rest of the world's possessions belongs to his heirs.
However, some other commentators have explained that the meaning of the second sentence is that whatever Allah has given you, make use of it for the Hereafter, without loosing sight of your needs in this world. In other words do not become a pauper by giving away everything in charity. Instead, retain something for your own needs as well. Under this explanation, 'your share in the world' means one's own needs in this world.