What is the obligation upon those who are sane and have attained puberty in Islam?

Allah has made Islam the religion of Allah with which happiness and salvation (is attained). If the 'Abd (worshipper) holds onto it and is steadfast upon it, for him is Paradise and honour. And the efforts of the worshipper based upon something other than the Sunnah (of The Messenger ﷺ) in Salah (prayer), fasting, or other acts of worship will not benefit him. (Allah says) {Today I have perfected your religion for you, completed My favour upon you, and chosen Islam as your religion.} [Al-Mā'idah: 3] {Whoever seeks a way other than Islam, it will never be accepted from them.} [Āl 'Imran: 85] Therefore, it is mandatory upon all the mukallafin to hold onto Islam and to strive upon obedience to Allah. This is the path to salvation and happiness. Hence, moderation in (the religion of) Islam and treading upon it with less is better than striving greatly in something other than Islam and the Sunnah. There's no Hawl (change from one state/condition to another) or strength except with Allah!