The notion that there is a connection between this life and the events of both our previous existence and our future existence, follows from the Buddhist understanding of the natural law of cause and effect. For example, although we can speak of yesterday's weather and today's weather as distinct, today's weather is inextricably linked with the weather patterns of yesterday. Even at the bodily level, in the case of our physical health for example, we know that events in the past affect the present and those of the present the future. Similarly, in the realm of consciousness the Buddhist view is that there is also this same causal continuum between the events of the past, present and future.
H H Dalai Lama --Tibetan Book of the Dead