The fourth cup of wine represents God’s fourth declaration of redemption: “I will claim you for me as a people, and I will be your God

בָּרוּךְ אַתָּה יְיָ, אֱלֹהֵינוּ מֶלֶךְ הָעוֹלָם, בּוֹרֵא פְּרִי הַגָּפֶן
Baruch atah, Adonai, eloheinu melech ha’olam, borei pri hagafen.

Blessed are you, Adonai our God, Ruler of the universe, creator of the fruit of the vine.

haggadah Section: Nirtzah
Source: Velveteen Rabbi's Haggadah for Pesach