From the scientific view, the theory of karma may be a metaphysical assumption -- but it is no more so than the assumption that all of life is material and originated out of pure chance
Surely if living creatures saw the results of all their evil deeds, they would turn away from them in disgust. But selfhood blinds them, and they cling to their obnoxious desires. They crave pleasure for themselves and they cause pain to others; when death destroys their individuality, they find no peace; their thirst for existence abides and their selfhood reappears in new births. Thus they continue to move in the coil and can find no escape from the hell of their own making.
The Buddhist, who thanks no man, who says "Do not flatter your benefactors," but who, in his conviction that every good deed can by no possibility escape its reward, will not deceive the benefactor by pretending that he has done more than he should, is a Transcendentalist.
From a Buddhist point of view, the actual experience of death is very important. Although how or where we will be reborn is generally dependent on karmic forces, our state of mind at the time of death can influence the quality of our next rebirth. So at the moment of death, in spite of the great variety of karmas we have accumulated, if we make a special effort to generate a virtuous state of mind, we may strengthen and activate a virtuous karma, and so bring about a happy rebirth.
Jnana, bhakti, yoga and karma - these are the four paths which lead to spiritual freedom. One must follow the path for which one is best suited. But in this age, special stress should be laid on karma yoga.
The universe that we inhabit and our shared perception of it are the results of a common karma. Likewise, the places that we will experience in future rebirths will be the outcome of the karma that we share with the other beings living there. The actions of each of us, human or nonhuman, have contributed to the world in which we live. We all have a common responsibility for our world and are connected with everything in it.