If you sincerely believe in the Buddha's teachings on causality, karma, rebirth, and the four noble truths, you will tend to be more responsible and compassionate.

"So instead of an empirical proof for his teaching on karma, the Buddha offered a pragmatic proof: If you sincerely believe in his teachings on causality, karma, rebirth, and the four noble truths, how will you act? What kind of life will you lead? Won’t you tend to be more responsible and compassionate? If, on the other hand, you were to believe in any of the alternatives — such as a doctrine of an impersonal fate or a deity who determined the course of your pleasure and pain, or a doctrine that all things were coincidental and without cause — what would those beliefs logically lead you to do? If you acted consistently in line with them, would they allow you to put an end to suffering through your own efforts? Would they allow any purpose for effort at all? If, on the other hand, you refused to commit to a coherent idea of what human action can do, would you be likely to pursue a demanding path of practice all the way through to the end? This was the kind of reasoning that the Buddha used to inspire faith in his Awakening and in its relevance to our own search for true happiness."

~ Thanissaro Bhikkhu "Faith in Awakening"