Tafsir of An-Nisa' 4:76

"Those who believe fight in the cause of Allah" is an interpolated statement brought forth to encourage the believers and entice them toward Jihad. It means: the believers fight only for the sake of Allah the Exalted—the path that leads to Him, the Almighty—and for the exaltation of His word. Thus, He is their Ally and their Helper, inevitably.

"And those who disbelieve fight in the cause of Taghut," which refers to that which leads to Satan, namely disbelief. Therefore, they have no helper other than him.

"So fight against the allies of Satan." Since the matter is as stated—that you are allies of Allah the Exalted and they are allies of Satan—then you will surely overcome them, for:

"Indeed, the plot of Satan has ever been weak." It is weak in and of itself; so how could it be otherwise when measured against the power of Allah the Exalted? "Those who fight in His cause," while He, Glorified be He, is your Ally—and He did not address the demonstration of the power of His Majesty, as its manifestation is self-evident.

The benefit of "has ever been" (kana) is to emphasize that his plot has been weak since the time it existed. It is also said that it carries the meaning of "has become," i.e., it became weak through Islam. Others have said it is redundant, but that is of no substance.