Tafsir Ibn Kathir -> Surah Az-Zumar -> Allah is Sufficient for His Servant Allah says:

﴿أَلَيْسَ اللَّهُ بِكَافٍ عَبْدَهُ﴾

(Is not Allah Sufficient for His servant) Some of them read it "His servants.'' It means that Allah is Sufficient for the one who worships Him and relies upon Him.

﴿وَيُخَوِّفُونَكَ بِالَّذِينَ مِن دُونِهِ﴾

(Yet they try to frighten you with those besides Him!) means, the idolators tried to scare the Messenger of Allah with their idols and gods which they called upon besides Allah out of ignorance and misguidance. Allah says:

﴿وَمَن يُضْلِلِ اللَّهُ فَمَا لَهُ مِنْ هَادٍوَمَن يَهْدِ اللَّهُ فَمَا لَهُ مِن مُّضِلٍّ أَلَيْسَ اللَّهُ بِعَزِيزٍ ذِى انتِقَامٍ ﴾

(And whom Allah sends astray, for him there will be no guide. And whomsoever Allah guides, for him there will be no misleader. Is not Allah Almighty, Possessor of Retribution) meaning, whoever relies on Him and turns to Him, will never be forsaken, for He is the Almighty Who cannot be overwhelmed by another, and there is none more severe than Him in exacting retribution on those who disbelieve in Him, associate others in worship with Him and resist His Messenger .