Imam al-Nawawi's 40 Hadith have come to be known as the most comprehensive, and holistic, compilation/collection of hadith of the Prophet Muhammad ﷺ that convey the essence of Islam.
Imam al-Nawawi's collection of 40 Hadiths is one of the most important collections of hadiths we have today. He actually compiled a total of 42 hadiths for this collection, not 40. Allah granted him blessing and success in his work so that he could make great contributions to Islam before passing away at a relatively young age.
The Imam was a scholar in many different disciplines of Islamic studies. The vastness of his works in these different areas is so great that if an individual decides to study fiqh, hadith, spirituality, or Quran; one would need to pass through Imam al- Nawawi. Along with the 40 Hadiths, he authored Riyad al-Saliheen, Al-Adhkar, and commentary of Sahih Muslim and Sahih Bukhari.