Why are the Sunan given precedence over the Fara'id in wudu', such as rinsing the mouth before washing the face?

The فقهاء (jurists) have mentioned wisdoms for the precedence of washing the hands, rinsing the mouth, and sniffing water into the nostrils in ablution, before washing the face. Among these is to ascertain the description of the water and that it is purifying. If the person performing ablution washes his hands, he sees the water; if he rinses his mouth, he tastes it; and if he sniffs water into his nostrils, he smells it. Thus, he discerns its characteristics (color, taste, and smell). Whether we comprehend the wisdom or not, what is obligatory is submission to the ruling of Allah and His Messenger; because, "And it is not for a believing man or a believing woman, when Allah and His Messenger have decided a matter, that they should [thereafter] have any choice about their affair. And whoever disobeys Allah and His Messenger has certainly strayed into a clear error" (Al-Ahzab: 36).