We have no better explanation available than prarabdha karma for the skewed ways things happen in our lives, which do not seem to fit into any logical pattern. The oft repeated question “why good people suffer and evil ones seem to enjoy life and why life is so unfair ?” cannot be answered convincingly without bringing the concept of Karma and rebirth.
In fact, this question has not been tackled in Abrahamic religions. Only Hinduism (and its offshoots Buddhism and Jainism) Karma and rebirth theory has been evolved apparently out of very logical analysis and through the insights of rishis.
And Karma theory offers consolation and a fair degree of resignation to surrender and accept divine will. If I am suffering in my life currently for no apparent fault or mistake or blunders or evil acts that I ever committed in this life, then I can console myself “Okay! I must have done something really evil in my previous births; so, it is God’s wish that I suffer my prarabdha now. God knows when to end this this suffering. I can only pray to him to relieve me from this; let His will be done” Such a surrender brings in peace of mind considerably.
Also accepting karma theory helps a lot in being watchful of our actions. “If I am suffering now on account of my evil acts in previous births, it means I will definitely suffer for any evil acts that I commit now probably much later in this life when I least expect it or in my next births. Why create trouble for myself? Let me abstain from doing this”. We also tend to engage in good and unselfish acts because saints promise us that the punya we acquire this way can potentially lessen the impact of the evil karmas of the past.
Thus a faith in Karma and belief in God as a dispenser of Karma helps us in leading a more peaceful life.
Our Karma cycle will only end when all our actions are done without any expectation of fruits. That is Karma yoga. For a Jnyani, who has realized himself, there are no fetters of karma. But some scriptures say that even Jnyani will have to suffer because of his prarabdha (effects of karma done in previous births) since he has obtained this body basically to exhaust his prarabdha.
But Bhagavan Ramana Maharshi disputes this idea. he says that a Jnani is free from all the three karmas (Sanchita, prarabdha and agamya karmas) . A jnani is one who has annihilated his mind; he is free from the concept that he is the body. Any prarabdha can work on body-mind only and when the Jnani is free from association with them, where is the question of prarabdha working on him? Asks Ramana Maharshi.
So, the final answer is this: The purpose of human birth is to attain oneness with our Atman (or God). Once we succeed in it, we get freed from karma and rebirth. Till then, we are caught in the samsara and come back again and again in new bodies to enjoy and suffer our fruits of karma.