Sacred status of hadith/sunnah in Islam
The primary sources of revelation in Islam are the Quran and Hadith/Sunnah. Quran explicitly orders the Muslims to obey and follow the Prophet's teaching and example when learning the book: "Allah did confer a great favour on the Believers when He sent among them a Messenger from among themselves, who rehearses to them the Signs of Allah, purifies them, instructs them in Scripture, and teaches them Wisdom, whereas previously they had been in plain error."  Here, and many other places in the Quran, we are informed about the importance of Hadith & Sunnah because the entire practice of the Quran and how to live by it is found in the life of the Prophet ﷺ. Since Allah ﷻ promises in ‘Al Quran 15:09’ that He has protected the message of guidance from all corruption till the day of judgment therefore His commandment to follow Prophetic teachings also hold exact same surety of protection.
The role of Isnad in hadith preservation
The hadith literature is a sacred tradition alongside Quran and the key to this sacredness lies in something called Isnad which basically means "chain of transmission". An Isnad contains a list of narrators who memorized and transmitted a hadith through a chain, that directly reaches all the way back to the sacred person of the Prophet ﷺ. For example lets say Imam Zaid memorized and wrote down a hadith he heard from his teacher Imam, who learned and memorized from his teacher a Companion, who directly met and heard from the Prophet ﷺ. Now when Imam Zaid will go and teach it to his students they will memorize the tradition, write it down and in turn will teach to their students. Through this process not only the hadith got memorized by who were taught but also transmitted from generation to generation, oral and in writing, linked with a chain that reaches back all the way to the Prophet’s sacred personality, who himself was recipient of revelation from Allah ﷻ through Angel Jibraeel (alaihi salaam). But there is one major sacred & spiritual factor guiding the isnad process. Nazim Bakhsh, quotes in his writing Shaykh Hamza Yusuf, a leading Islamic scholar, who gives an overview of how scholars have made use of Isnad process from generation to generation through something called Ijaza: "Shaykh Hamza Yusuf, has often said that isnad is the secret of this Ummah and a gift from Allah. Without isnad the entire tradition could very well collapse. The system of ijaza (teaching licenses) is intricately linked to isnad in that one takes his knowledge from noble men and women who took their knowledge from those who took their knowledge from those….all the way back to that model community (companions) and to the blessed Messenger himself, whose knowledge, without a shadow of doubt, came from the Lord of the Divine Throne through his messenger, the Angel Gibril (Gabriel), upon him be peace.”  Ijazas are teaching licenses given by a Sheikh, well versed and knowledgeable in Islam to those of his students whom he approves to be fit of transmitting hadith and other knowledge directly from himself. This has maintained the transmission process called isnad not only on the academic level but also on a spiritual level.
As discussed earlier, Isnad is part of a wider process called ilm al hadith (sciences of hadith), that maintains the unanimous position of the Islamic scholars who not only recorded & memorized the hadith but also scrutinized them making it clear which of them fall under category of sahih (authentic), mursal (interrupted), dhaeef (weak), munkar (rejected), mawdoo (fabricated), in terms of their chain of narrators. They were familiar with who the forgers were and who were the unknown narrators, who should not be considered fully trustworthy in the chain. All of that is due to the position and importance of the Prophet Muhammad ﷺ, as the seal of all the Prophets and leader of humankind. Hence it is these sacred factors that have guided the systematic process of hadith collection and preservation due to which forgeries and interpolations have not been able to be attributed to him and to be accepted by the majority consensus of Islamic scholars.
 Al Quran 3:164 - Asad Translation
 Baksh, Nazim. 2015. In The Spirit of Tradition. January 5th. Accessed January 7th, 2020. http://masud.co.uk/in-the-spirit-of-tradition/.