The Prophet (saas) made it known that the Qur'an was sent down as guidance and good news for the Muslims

the prophet (saas) said that the qur'an led people to the true path, and advised people to take it as their guide. some of the verses on that subject are:

say: "the purest spirit has brought it down from your lord with truth, to make those who believe firm, and as guidance and good news for the muslims." (surat an-nahl: 102)

say: "if i am misguided, it is only to my detriment. but if i am guided, it is by what my lord reveals to me. he is all-hearing, close-at-hand." (surah saba': 50)

this is why the prophet (saas) placed great importance in teaching the qur'an:

"acquire the knowledge and impart it to the people. learn the qur'an and teach it to the people; for i am a person who has to depart this world."42