In Tibetan Buddhism, the lunar month of Saga Dawa (which in 2017 is May 26 to June 24)  is the most important time of year; in other Buddhist traditions it is called Vesak, Vesākha (Pali), Vaiśākha (Sanskrit), Buddha Purnima, etc. 

During this four week time all Buddhists honor the birth, enlightenment, and death of the Buddha Shakyamuni by intensifying their spiritual practices and acts of generosity. In this lecture we will discuss why this is important and how it relates to each of us, since no matter our beliefs, we have our own inner Buddha, and the potential to become a Buddha. That potential is called Budda Nature (Buddhadhatu, tathagatagarbha, etc), and the best way to develop it is through the full understanding and expansion of Bodhichitta. 

“…hidden within the kleshas [negative mental traits] of greed, desire, anger, and stupidity there is seated augustly and unmovingly the tathagata's wisdom, the tathagata's vision, and the tathagata's body. Good children, all beings, though they find themselves with all sorts of kleshas, have a tathagatagarbha that is eternally unsullied, and that is replete with virtues no different from my own.” —Tathagatagarbha Sutra

"Whatever joy there is in this world All comes from desiring others to be happy, And whatever suffering there is in this world, All comes from desiring myself to be happy.

But what need is there to say much more? The childish work for their own benefit, The Buddhas work for the benefit of others. Just look at the difference between them!" —Shantideva