Tafsir of Al-A'raf 7:151

(He said) — this is a new sentence initiated by a question arising from the account of the apology, as if it were said: "What did Moses, peace be upon him, say when his brother apologized?" It is then said: He said: "My Lord, forgive me" — for what I did to my brother before the truth of the situation was revealed, for the good deeds of the righteous are the misdeeds of those brought near — "and my brother," if he was characterized by what is considered a sin for him in the matter of those wrongdoers. In this coupling, there is a way to appease him, peace be upon him, and to ward off any gloating over him. It is also said that he sought forgiveness for himself to satisfy his brother and to show those who were gloating that he was pleased with him, so that their gloating would not be fulfilled. He sought it for his brother to signal that he was in need of forgiveness, as he was obligated to fight them, though there is a reservation regarding this that is not hidden.

"And admit us" — both of us — "into Your mercy" — the expansive one, through an increase of Your grace upon us. This is what is required by the pairing with forgiveness, and the shift from "have mercy on us" to what was mentioned.

"And You are the Most Merciful of the merciful."

There is no wonder in us being joined in the series of Your expansive mercy in this world and the Hereafter. This sentence is a parenthetical conclusion, confirming the content of what preceded it. Some have claimed that it contains an indication that He, glory be to Him, answered his prayer, though there is obscurity in that.