Remember the day of the Sabbath - that teaches kiddush of the day, but how do we know to make kiddush at night too? In fact, we should really be asking about the day and taking the night as the given. Until another approach is presented - for the source of kiddush at night. Note that the Gemara here is sussing out what is going to be the authoritative approach. Also, what kiddush should be made during the day, such that it will be different from that recited at night. R. Ashi in Mehoza is asked to make "Kiddusha Rabbah" - and he figures it out what they mean on the spot. Indeed, the wise one's eyes are in his head. Unusual, here, is that we see the inner workings of R. Ashi's thought process.