Sri Ramakrishna used to explain beautifully the theory of reincarnation (rebirth) using a parable. The theory of Karma is deeply linked to this idea.
There was a man who was practising Sava Sadhana (Tantrik practice using Sava or corpse as seat for meditation). He was worshipping the Divine Mother in a deep forest. He had struggled hard and with great difficulty procured the items necessary for the worship. Soon after he sat for meditation, he saw several terrible visions and finally a tiger attacked and killed him. Another man passing by happened to see the tiger and had climbed a tree to protect himself. After the tiger went away, he got down from the tree and seeing the arrangements for worship at hand seated himself on the corpse and began the worship. In no time he had the vision of the Divine Mother who being pleased with his worship wanted to grant him a boon. The man bowed with deep devotion and told the Divine Mother, “Mother! I am speechless and amazed by your action. The other person had worked very hard and gathered the ingredients for your worship, but you did not bless him with your vision. But, I who am not really familiar with this worship, with very little effort have received so much of your grace.” The Divine Mother said with a smile, “You do not remember your past births during which you had tried to propitiate me through intense austerities. It is because of those austerities that you have been blessed with my vision. Now ask for a boon.”
The effects of the karmas or actions done in the past births are not too difficult to discern. Quite often man feels baffled by incidents of death, deprivation, etc leading to intense sorrow and sufferings. The law of karma is perhaps the most logical answer to the puzzles of life.