Allah's statement,

﴿فَأَعْرِضْ عَن مَّن تَوَلَّى عَن ذِكْرِنَا﴾

(Therefore withdraw from him who turns away from Our Reminder), means, stay away from those who turn away from the Truth and shun them,

﴿وَلَمْ يُرِدْ إِلاَّ الْحَيَوةَ الدُّنْيَا﴾

(and desires nothing but the life of this world.) meaning, whose aim and knowledge are concentrated on this life; this is the goal of those who have no goodness in them,

﴿ذَلِكَ مَبْلَغُهُمْ مِّنَ الْعِلْمِ﴾

(That is what they could reach of knowledge.) meaning, seeking this life and striving hard in its affairs is the best knowledge they have acquired. There is also the reported supplication:

«اللْهُمَّ لَا تَجْعَلِ الدُّنْيَا أَكْبَرَ هَمِّنَا، وَلَا مَبْلَغَ عِلْمِنَا»

(O Allah! Make not this life the greatest of our concerns nor the best knowledge that we can attain.) Allah's statement,

﴿إِنَّ رَبَّكَ هُوَ أَعْلَمُ بِمَن ضَلَّ عَن سَبِيلِهِ وَهُوَ أَعْلَمُ بِمَنِ اهْتَدَى﴾

(Verily, your Lord is He, Who knows best him who goes astray from His path, and He knows best him who receives guidance.) meaning, He is the Creator of all creatures and He knows whatever benefits His servants. Allah is the One Who guides whom He wills and misguides whom He wills, and all of this indicates His power, knowledge and wisdom. Certainly, He is Just and never legislates or decrees unjustly.

﴿وَلِلَّهِ مَا فِى السَّمَـوَتِ وَمَا فِى الاٌّرْضِ لِيَجْزِىَ الَّذِينَ أَسَاءُواْ بِمَا عَمِلُواْ وَيِجْزِى الَّذِينَ أَحْسَنُواْ بِالْحُسْنَى - الَّذِينَ يَجْتَنِبُونَ كَبَـئِرَ الإِثْمِ وَالْفَوَحِشَ إِلاَّ اللَّمَمَ إِنَّ رَبَّكَ وَسِعُ الْمَغْفِرَةِ هُوَ أَعْلَمُ بِكُمْ إِذْ أَنشَأَكُمْ مِّنَ الاٌّرْضِ وَإِذْ أَنتُمْ أَجِنَّةٌ فِى بُطُونِ أُمَّهَـتِكُمْ فَلاَ تُزَكُّواْ أَنفُسَكُمْ هُوَ أَعْلَمُ بِمَنِ اتَّقَى ﴾

(31. And to Allah belongs all that is in the heavens and all that is on the earth, that He may requite those who do evil with that which they have done, and reward those who do good, with what is best.) (32. Those who avoid great sins and Al-Fawahish (immoral sins) except Al-Lamam -- verily, your Lord is of vast forgiveness. He knows you well when He created you from the earth (Adam), and when you were fetuses in your mothers' wombs. So, ascribe not purity to yourselves. He knows best him who has Taqwa.)