The Messiah IS "the prophet we must hear and obey"
Deuteronomy 18:18-19, "I will raise up for them a Prophet like you from among their brothers, and I will put My words in His mouth, and He will tell them everything I command Him. Whoever will not listen to My words, which He speaks in My Name, I will judge him for it"
"listen" is word #8085 שָׁמַע shama` {shaw-mah'}
Brown-Driver-Briggs (Old Testament Hebrew-English Lexicon)
A primitive root; to hear intelligently (often with implication of attention, obedience, etc.; causatively to tell, etc.)
Hebrew Word Study (Transliteration-Pronunciation Etymology & Grammar) - 1) to hear, listen to, obey