To study a religion is to study the mind. The Buddha did not teach many things. When he taught the 5 ascetics, he told them to contemplate the body and its 32 organs and to analyse all its elements.
The Buddha also pointed out to them that the body was born from cooked rice, fresh cakes, nuts, sesame, butter, earth, water, fire and wind. All these factors were analysed by him. The next step was to view the body clearly, so clearly that they could see that the body starts to decay and eventually disintegrates. As the result, they would have Samadhi as an object of consciousness which consisted of applied thought, sustained thought, joy, bliss, and one-pointedness of mind.
He continued to elaborate on the Cause of Suffering (Samudaya). Suffering takes place from citta (mind) and Viññāna (consciousness). Craving can be stopped by having sharp awareness. At first this teaching was for the 5 ascetics. Later on Ananda and Sariputta (two of the chief disciples) were taught the same thing. Ordinary people were also taught the same thing.