question #3 Sahih Muslim 15c, Book 1, Hadith 18 : What is the significance of adhering to what is lawful and avoiding what is forbidden in Islam?

Shall I enter Paradise in case I say the obligatory prayers, observe the (fasts) of Ramadan and treat that as lawful which has been made permissible (by the Shari’ah) and deny myself that what is forbidden, and make no addition to it? He (the Holy Prophet) replied in the affirmative. He (the inquirer) said: By Allah, I would add nothing to it.