بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ
How would the slaves (i.e. Mankind and Jinn) know what Allaah loves and what Allaah hates?
They know it through Allaah sending the Messengers and revelation of the Books [i.e. the Zaboor, Tawraat, Injeel, and the Qur’aan (the final revelation)]— commanding what Allaah loves and is pleased with; and forbidding what Allaah hates and disdains. And by way of this, Allaah’s irrefutable proofs are established against them (i.e. Mankind and Jinn) and His Perfect Wisdom is manifested.
Allaah (The Most High) said:
رُّسُلاً۬ مُّبَشِّرِينَ وَمُنذِرِينَ لِئَلَّا يَكُونَ لِلنَّاسِ عَلَى ٱللَّهِ حُجَّةُۢ بَعۡدَ ٱلرُّسُلِۚ
”Messengers as bearers of good news as well as of warning in order that mankind should have no plea against Allah after the Messengers.” [4:165]
And Allaah (The Most High) said:
قُلۡ إِن كُنتُمۡ تُحِبُّونَ ٱللَّهَ فَٱتَّبِعُونِى يُحۡبِبۡكُمُ ٱللَّهُ وَيَغۡفِرۡ لَكُمۡ ذُنُوبَكُمۡۗ وَٱللَّهُ غَفُورٌ۬ رَّحِيمٌ۬
”Say (O Muhammad to mankind): “If you (really) love Allah then follow me (i.e. accept Islamic Monotheism, follow the Qur’an and the Sunnah), Allah will love you and forgive you of your sins. And Allah is Oft-Forgiving, Most Merciful.” [3:31]
[Source: 200 hundred questions and answers on the Islamic creed by Haafidh Hakami (rahimahullaah) page: 14]