Importance of dhikr (remembrance of Allah)

وَمَن يَعْشُ عَن ذِكْرِ ٱلرَّحْمَـٰنِ نُقَيِّضْ لَهُۥ شَيْطَـٰنًا فَهُوَ لَهُۥ قَرِينٌ

And whoever is blinded from remembrance of the Most Merciful - We appoint for him a devil, and he is to him a companion.