Surah Al Isra Tafseer

Allah says:

رَّبُّكُمْ أَعْلَمُ بِكُمْ

Your Lord knows you best;

O mankind, meaning, He knows best who among you deserves to be guided and who does not deserve to be guided.

إِن يَشَأْ يَرْحَمْكُمْ

if He wills, He will have mercy on you,

by helping you to obey Him and turn to Him.

أَوْ إِن يَشَأْ يُعَذِّبْكُمْ وَمَا أَرْسَلْنَاكَ

or if He wills, He will punish you. And We have not sent you (- O Muhammad -).

عَلَيْهِمْ وَكِيلً

as a guardian over them.

meaning, `We have sent you as a warner, so whoever obeys you, will enter Paradise and whoever disobeys you, will enter Hell.