Tafsir of Ash-Shura 42:31

(And you will not cause failure upon the earth), meaning: you will not render Allah, Glorified and Exalted be He, unable to afflict you with calamities for what your hands have earned, even if you flee to the corners of the earth in every possible way. It is also said: The meaning is that you cannot frustrate those upon the earth from among His soldiers, so how could you frustrate the One in the heavens?

(And you have none other than Allah as a protector), meaning: a guardian of mercy who would have mercy upon you when calamities strike you. It is also said: [A guardian] who would protect you from them, or (nor a helper), meaning: one who would repel them from you.

The sentence serves as a confirmation of His saying, Exalted is He: (And He pardons much), meaning: verily, Allah, Exalted be He, pardons many calamities, for you have no power to render Him unable—Glorified be He—so that you might escape what He has decreed upon you. Furthermore, you have no guardian of mercy other than Him, Mighty and Majestic be He, to show you mercy when they strike you, nor any helper other than Him to assist you against them. For this reason, it has been narrated from Ali—may Allah, Exalted be He, ennoble his face—that this is the most hopeful verse in the Quran for the believers.

The aspect of hope is strengthened by what has been said: that the meaning of (And you...) etc., is "you will not render Allah, Exalted be He, unable to repel your calamities," meaning that He, Glorified be He, is capable of doing so.