Four Ennobling Truths
The Four Ennobling Truths are considered to be the first teaching by the historical Buddha following his Awakening. If they are not the most important teaching the Buddha gave, they certainly form the basis for all the other teachings which followed. Regardless of how much one has studied it, this teaching never gets old. Each time we return, we are coming from a different place in our lives. It's like an old friend who we never tire of seeing because each time we come to it we learn something new.