The first assurance is based on the existence of rebirth and causality. If one commits wrongdoing, then one will have a bad rebirth. If one does good deeds, one will have a good rebirth. It is because of this premise that many people strive to live a moral, selfless, and caring life. We all wish to end our suffering and to find happiness. But an awakened being who has eliminated the three poisons and who is thoughtful and caring goes one step further—this being wishes to help others eliminate suffering and attain happiness as well.
It is difficult to be a truly compassionate person. It takes many, many lifetimes to become such a person. Believing in the reality of karma and rebirth, we understand that immorality and selfishness will lead us to miserable rebirths, unable to help ourselves or others. We have already wasted more lifetimes than we can count. Failing to practice the Buddha’s teachings, we will waste many more. The only way to truly help people is to create and accumulate good fortune. Good fortune includes a safe place to live, enough material resources, skills, wisdom, time, and good health. These are the conditions found in a good rebirth.
But only by using our good conditions to benefit others can we continue to generate more good conditions for future use. If we selfishly use the goodness we have created to make our own lives more pleasurable and neglect the needs of others, we will exhaust that goodness and at some point face painful situations.