וְאֶת־בְּרִיתִ֖י אָקִ֣ים אֶת־יִצְחָ֑ק אֲשֶׁר֩ תֵּלֵ֨ד לְךָ֤ שָׂרָה֙ לַמּוֹעֵ֣ד הַזֶּ֔ה בַּשָּׁנָ֖ה הָאַחֶֽרֶת׃
내 언약은 내가 명년 이 기한에 사라가 네게 낳을 이삭과 세우리라
Chizkuni
למועד הזו לשנה האחרת "at this season next year;" Rav Huna said in the name of Rav Idi: that year was a leap year [in which an additional month of Adar was added before Nisan], meaning "מועד" and "מועד" was one year apart from each other, and he calls it "next year" because of the additional month it has in it.
Da'at Zekenim
ואת בריתי אקים את יצחק, “and My covenant I will establish with Yitzchok;” the word אקים is to be understood as an acrostic from the phrase: אשר קידש ידיד מבטן, a phrase recited after every circumcision, meaning: “who is well beloved already when he emerges from the womb.”
Kitzur Ba'al HaTurim
"I will establish my covenant with Isaac" - "אקים" can be interpreted as a hint that God sanctified His beloved friend (Isaac) from the womb.