Why does the Torah insert "Temimim Yih?yu lachem" here?
Rashi: To teach us that the Nesachim ? like the animals - must be without blemish, disqualifying wine in which mold appears. 1
Oznayim la'Torah (in Pasuk 20): Chazal Darshen from here that also the flour and the oil must be without blemish, the flour - without worms or 'dust' and the oil - with its taste intact and not having turned bitter. 2
The Sifri adds Nesachim that are Chaser ve'Yeser (less or more than than the required Shi'ur). See Torah Temimah, note 57, who elaborates, and who explains, inter alia, why the Torah teaches the Din of blemishes in the Nesachim specifically on Shavu'os. The Oznayim la'Torah offers a similar explanation.
See also Oznayim la'Torah on the current Pasuk, who also declares Pasul sweet wine and wine that has been smoked or cooked, and who elsborates.
