Karma?...

What do they say? "You are suffering now because in previous life you did wrong. You suffer so you may understand, taste the evil you created". What's the purpose? "To stop doing it anymore in this life". Probably to not doing it in the future life, but unfortunately in the next life you wouldn't remember anything just like you don't remember anything in the present life. Who knows?

Does lives are really following the series of karmic punishment - karmic reward - and so on.?

No. Humans are not here to suffer. I have the consciousness to understand the mistakes I did, am doing and would do, and a strong resolution and unconditional choice not to do it is completely enough. And instead of wasting time in agony and torture which is not constructive at all, one may start creating and enriching the environment he belong to.

Even if I accept the reincarnation of souls as a complete truth, I think that if I understand I committed evil before, If I start doing good God, Nature and the whole world would be much interested and grateful of me, rather than suffer, pain and be a victim of suffering.

Misfortunes comes from misunderstanding/incompetence/refusal to transform energy/information/matter from the areas of abundance in your life, into energy/information/matter to the areas of shortage in your life.