The law of three, is what ever you send out into the universe will come back to you 3 times more than you sent out...e.g if you send out loving thoughts and do good deeds, you will recieve these things back 3 fold, or if you where to send out hurtful thoughts or do bad deeds then you will also recieve these back 3 fold.
(these are my personal beliefs and not all will agree with them)
The law of three is not to be mistaken for the Law of Karma though, as Karma works on a totally other level, Karma is actually there to help or souls advance by learing lessons in each incarnation if we have chosen to incarnate again, and there will be some of us that properly actually dont have any karmic issues to work through, and others who may have choosen a lot of karmic issues in their incarnation and the most who choose mulitple karmic issues are wanting to learn and develop their souls ascension a little quicker than others would chosse to do.
But not all people believe in the 3 fold law or Karma again its all down to a persons free will to believe what is right for them.
Hm.. If it goes back again to me in 3folds, I better carefully choose my thoughts :)
I believe in karma. It's the law of universe. Despite you belief it or not, it's still going to work because it's the law. Just like if someone don't believe in law of gravitation, he jumped from 10floor building, still he'll go down. I believe in karma because I often experience what I say or do, specially the bad one, not long after that there'll be someone say or do the same thing to me.
I also belief in past life / reincarnation. What we are now (where we born, what we have) is the result what we have done in the past.
I have read a book "many lives, many master" by Brian weiss. It's a very intersting book. He said in his book that each person has something to learn in each life. I think what I have to learn in my current life is patience :) still trying though hehhe...
