The Qur'an enjoins absolute obedience to the Messengers, for they have been sent to guide people to truth in every sphere of their lives. Our loyalty is to God, Who has sent His Messenger and told us to obey him, and not to that man personally: We have not sent a Messenger save to be obeyed by God's leave (4:64), and: O you who believe! Obey God and His Messenger, and do not turn away from him (8:20).
Obedience to God means unconditional obedience to what has been revealed in the Qur'an. Obedience to the Messenger means following his way of life as closely as possible by obeying what is enjoined and prohibited in the Qur'an and by the Messenger. The Sunna is a comprehensively detailed account of his life. He told his community: "Take care! I have been given the Book and its like together with it." 
As stated in 8:20, Muslims must not turn away from the Messenger. Therefore, disobeying, belittling, or criticizing the Sunna amounts to heresy or even apostasy. Many other verses emphasize the necessity of following the Sunna, such as: O you who believe! Obey God and obey the Messenger and those in authority from among you (4:59). The verse stresses obedience to God and to the Messenger. The repetition of obey in the imperative mood indicates that the Messenger is authorized to command or forbid, and that Muslims must do what he says. Besides, where obedience to those Musims in authority is ordered, the Prophet has a far greater right to be obeyed.
Another verse states: Obey God and His Messenger and do not dispute with one another, lest you should be dissolved (dispersed) and your strength fade away; and be steadfast (8:46). Muslim strength and unity lie in submission to God and His Messenger. The Messenger established the Sunna by living the Qur'an, which means that it is the only way his community can follow. Based on this, we can say that the Sunna is both more comprehensive than the Qur'an and indispensable for leading an upright life in Islamic terms.
Muslims can obey God and show their love for Him only by obeying the Messenger or by following his Sunna: Say (O Muhammad): "If you love God, follow me so that God loves you" (3:31), Surely there is for you in the Messenger an excellent example for him who aspires to God and the Hereafter, and mentions God oft (33:21), and many other verses. Those who claim to love God or that God loves them, despite their non-adherence to the Sunna, are seriously deluded and astray.
Muslims must cling to the Sunna if they want to remain on the Straight Path and avoid deviation. For example: One day a woman said to 'Abd Allah ibn Mas'ud: "I have heard that you call down God's curse upon women who tattoo their bodies, pluck their facial hair, force their teeth apart in order to look more beautiful, and who change the creation of God." Ibn Mas'ud answered: "All of this is found in the Qur'an." The woman objected: "I swear by God that I have read the entire Qur'an, but I couldn't find anything related to this matter." Ibn Mas'ud told her: "Our Prophet called God's curse upon women who wear wigs, who join somebody's hair to theirs, and who have tattoos on their bodies. Haven't you read: Whatever the Messenger brings you, adopt it; whatever he forbids you, refrain from it (59:7)?" 
The Qur'an also declares: Nay, by your Master, they will never become believers until they choose you as judge to settle the matters in dispute between them (4:65).
 Muslim, "Libas," 120.