Here is the Pali text translated in English and Vietnamese. It is true that it is very neccessary for Buddhists to grasp the basic foundation of teachings. And these teachings can be found in Pali texts of Theravada. To avoid using the term which the other vehicle does not like. We will use Theravada. From my understanding, you have to build your foundation through basic teachings, and basic teachings are in the line of ethical living. Now if you were Chinese and had lived in China a long time ago, there is no need for you to study Pali texts because your foundation has been built through Taoism and Confuscianism which taught you well on ethical living, how to interact with one another, the environment, and such. Here you are now in the modern day, you have to start everything at the base. Precepts, vows, and such as 10 virtuous actions are what I am referring to...so it's important to keep in mind that the teachings of other vehicle are not excluded from Mahayana's teachings. It is also incorrect for people to assume that Mahayana does not understand teachings of the other vehicle. So Mahayana is inclusive.
As for 'mara cannot possess you if you live righteously', indeed mara represents non-righteousness so how can mara possess righteousness. For mara to possess you, you have to be compatible with it. For example during your advanced meditation, if a thought of arrogance arises, you will be immediately possessed by mara. Why? Arrogance and similar thinking are traits of mara. If you don't nurture evil thoughts, you will not be controlled by mara or turn into one. So becareful if you are interested in gaining superpowers and such, you can be easily possessed by demons as this interest is your weakness...to further explain this, when anger arises, immediately you will feel very uncomfortable because you are linked to suffering of hells. When you are happy, you are linked to joy of gods. When you recite Amitabha, you are at one with Amitabha and at peace at that moment.
What I explained above is the meaning of possession. Yes, everyday we are also possessed by greed, anger, and ignorance, the 3 karma of body, speech, and mind.
Thanks for reading