Tafsir of An-Nisa' 4:45

(And Allah is most knowing) than you, O believers, (of your enemies), among whom are these people. He has informed you of their enmity toward you and what they intend, so beware of them. The sentence is parenthetical, serving as emphasis and an explanation of the warning; otherwise, the all-knowing nature of Allah Almighty is already established. It is said: the meaning is that He, Exalted is He, is more knowing of their state and the outcome of their affairs, so do not pay them any heed and do not be preoccupied with them. (And sufficient is Allah as an ally) who manages your affairs and benefits you with whatever He wills, (and sufficient is Allah as a helper) who wards off their plotting and their evil from you. So, be content with His alliance and His support, do not care about them, and do not be in distress over what they plot. In this is a promise for the believers and a threat to their enemies; the sentence is also parenthetical.

The ba is additive in the subject of kafa (sufficient) to emphasize the attribution with what implies connection, which is the ba of attachment (ilṣāq). Al-Zajjaj said: This ba entered because the speech carries the meaning of "seek sufficiency in Allah." Waliyyan (ally) and naṣīran (helper) are in the accusative case as tamyīz (specification); it is also said they are in the state of ḥāl (adverbial condition). The repetition of the verb in both sentences, while expressing the Majestic Name, serves to emphasize His sufficiency, Almighty and Exalted is He, while intimating causality.