Related על ברכות 8:1

They mix him the first cup. Beit Shammai says, he blesses on the day and then he blesses on the wine, because the holiday is the direct reason for drinking the wine, and the holiday had already started when the wine was brought to the table. Beit Hillel says, he blesses on the wine and then he blesses on the day, because if we didn't have the wine we wouldn't be saying Kiddush on the holiday at all. Another explanation: the blessing on wine is regularly said and the blessing on the holiday is not. And the halacha is according to Beit Hillel.