The Prophet was a walking talking Qur'aan.
The Qu'raan is a Reminder, and Final Revelation. In it are unclear verses, of which need to be explained, and the Book is a book of guidance, which needs to be understood with the correct understanding, and not individual intereptaions. The Prophet was sent by Allah, and like all the Prophets and Messengers, was given the wisdom, Hikmah, by the One who sent him, and so was able to explain to the believers by way of speech, and act out the commandments within the revelations in the correct manner and with the correct undersanding. The way in which Allah intends good for His believers, and in which we can obtain Jennah.
It is imperative to follow his Sunnah. The proof is Allahs saying, "Obey Allah AND obey the messenger. Truly Allah will love you and forgive you your sins"
Allahs saying, " And We have sent down to you a reminder (Muhammad), that you may explain clearly to the people that which is sent down to them"
"He who obeys the Messenger has indeed obeyed Allh"
"What the Messenger gives, you take, and what he forbids you avoid"
"It is not for a believing man nor woman, that when Allah AND His messenger have judged in a matter, that they should have an option in thier decision, and whoever disobeys Allah AND HIs Messenger has strayed in clear error"
The Sunnah is Islam, and Islam is the Sunnah. It is not for Muslims to interpret Islaam to suit personnal desires. Other wise, what was the point of the Messenger being sent by Allah? Allahs saying, "Today I have perfected your religion for you, completed my favours upon you, and have chosen Islaam as your religion". Allah has said that the Revelation, and Islaam, is complete and perfected, and will be preserved and unchanged until the Final Day. We do not need to change any aspect of Islaam to suit our personnal desires, even when the intention is good. Indeed Muhammad said, "Every innovation is misguidance, and every misguidance leads to hell fire" He also said, "Whosoever invents a matter into this affair of ours (meaning the religion), then it will be rejected on the Day of Resurrection"
He also said, "He who does not follow my way, is not from me"
He also said, ".......The Muslims will split into 73 sects, all of them in the hell fire except one" Hs companions asked, "Who are the saved sect?" He replied, " That which I, and my companions are upon"
In one of Muhammads last sermons to the people, he spoke a lengthy speech warning and commanding his followers to stick to his way, "...Those of you who will live long, will see a great amount of splitting and differing.....so what is upon you is to stick to my Sunnah, and the Sunnah of my rightly guided companions, and hold onto it with your molar teeth...(meaning fight and struggle to keep hold of the Sunnah)....."
To just go by the Qu'raan without the understanding and explanation of Muhammad, then a person will no doubt fall into error. How many a times do we hear of Muslims carryingout atrocities and other lesser acts in the name of Islaam, when in reality they have no knowledge of what they do? They take verses from the Book and decide how to live them out by way of personnal, or political desire. These Muslims are ignorant, and misguided, even if the intention is good! Ibn Mas'oud, a great companion of the Prophet, when he came across a group of Muslims who were worshipping Allah in a manner in with the Messenger did not command, said, "How many intend good, but never reach it?" Did you know there are seven conditions of the Shahada? The very first condition is Knowledge! Knowledge repels ignorance, and a person can only have knowledge of Allahs religion if he studies the life and sayings of Muhammad.