וַהֲקִמֹתִ֤י אֶת־בְּרִיתִי֙ אִתְּכֶ֔ם וְלֹֽא־יִכָּרֵ֧ת כָּל־בָּשָׂ֛ר ע֖וֹד מִמֵּ֣י הַמַּבּ֑וּל וְלֹֽא־יִהְיֶ֥ה ע֛וֹד מַבּ֖וּל לְשַׁחֵ֥ת הָאָֽרֶץ׃
내가 너희와 언약을 세우리니 다시는 모든 생물을 홍수로 멸하지 아니할 것이라 땅을 침몰할 홍수가 다시 있지 아니하리라
Rashi
והקמתי AND I WILL ESTABLISH — I will give confirmation to my covenant; and in what consists this confirmation? “The sign of the rainbow”, as it goes on explaining at the end.
Chizkuni
והקימותי את בריתי, “I shall maintain My covenant as applicable, etc.” The reason why G-d’s promise not to bring on another deluge is repeated in the same verse, is to underline that even if the human race would again be guilty of similar conduct to that which had brought about the deluge, this covenant would not be considered by G-d as null and void.
Sforno
ולא יהיה עוד מבול לשחת הארץ, there will not ever again be the kind of catastrophe which will destroy the whole surface of the earth at the same time.