What are the most important and fundamental principles of all Divine Religions?

In reply to a question about the most important and fundamental principles of all Divine Religions, Imam Sajjad (AS) said: Inviting (people) to the truth, just judgement (acting on fair and unprejudiced judgment) and fulfilling the promise (covenant, treaty, contract, agreement, pact) [1].

[1] Khesaal, Page 113, Hadith 90.