True Reasoning of Mitzvos

Parshas Chukas calls the Parah Adumah "Chukas HaTorah," the law of the Torah, when we would expect the law of the Parah. Shlomo HaMelech worked to understand its reasons and gave up, yet a Gemara in Sanhedrin says it was knowing the reasons that led him to sin. Why would his admission be that he thought he understood, rather than that he trusted himself too much? And why does the Gemara silence someone who prays "have mercy on us as You do on the mother bird"? Food and its taste hold the thread.