Allaah (The Most High) said:
أَرَأَيْتَ مَنِ اتَّخَذَ إِلَٰهَهُ هَوَاهُ
Have you (O Muhammad) seen him who has taken as his ilah (god) his own desire?
[Soorah Al-Furqaan: Ayah: 43]
Imaam as-Saa’di (rahimahullaah) said: Are you not amazed by his (i.e. this person’s) state of affairs and you are looking at the misguidance he is upon, whilst he judges for himself that he is upon lofty stations?  Imaam Ibn Katheer (rahimahullaah) said: And whenever something is desirable and he sees it as (something) good according to his own desires, it becomes his religion (or creed, judgement, way of life and school of thought). 
 Tayseer Al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan
Al-Misbaah Al-Muneer Fee Tahdheeb Tafseer Ibn Katheer