Every one of our actions and feelings, as well as our thoughts, represents a cause, here and now, that triggers an effect. 
But as our life does not end when we leave the earth, those actions, feelings and thoughts, which are living, active realities, will continue to follow us not only into the world beyond, but also when we come back to incarnate again.
So reincarnation is merely the logical extension of the law of cause and effect.

And those who do not acknowledge that the person they are now, and what they are experiencing now, is influenced by who they were and what they experienced in former lifetimes – and also that what they are doing and experiencing in this lifetime will have repercussions in lives to come – will never understand anything about divine justice.

Omraam Mikhael Aivanhov – Cosmic Moral  Law, Vol.12, Complete Works