There is no such thing as "sin". Everything is really just a learning opportunity. Karma is basically a teaching tool.
If you are not able to learn a lesson in school - it is not a sin and the teacher will not punish you. She'll just repeat the lesson till you get it. Karma works in the same way - if you haven't learned the value of love, compassion, empathy, kindness, gratitude, etc, karma will repeat the lessons till you learn it.
For example: If someone cheats you out of your money - you'll feel bad and thus hopefully you'll never cheat anyone. If you do cheat someone - then karma will see to it that you are cheated again and again till you learn the value of honesty.
Similarly, if you are in a position of power and abuse that power - that means you do not know the value of love, compassion and justice. Karma needs to teach you the importance of these - so you will have to reincarnate in a lifetime where you will be at the receiving end of abuse of power - and then hopefully you will realise how important love compassion and justice are. You get a dose of your own medicine. If you still don't learn then the lesson will be repeated (no matter how many lifetimes it takes) till you finally learn it.
“Earth is a SCHOOL for learning duality and understanding “opposites,” which helps you fast track your spiritual growth. Reincarnation and freewill are the tools for this spiritual growth. For every fantastic lifetime of love, joy, and happiness, there has been an equally strong and negative emotional experience of devastation, hardship, pain, and suffering.
There are no such things as hell, the devil or satan; these are false manmade beliefs, which were created for explaining the unloving attributes of pain, suffering, chaos, and destruction created by early civilizations (infant souls). As souls, each one of you has had many different lifetimes on Earth. Before each incarnational cycle, you decide what lessons you want to learn, the basic requirements for your life and the type of polarized experiences you want to explore on Earth.
Reincarnation helps you master your lessons in duality. You have killed and been killed by others; you have been male and female, including mother, father, son, uncle, grandmother etc. You have been a soldier, warrior, villain, farmer, and artist. You have experienced suffering, disease, illness, poverty, pain, joy, love, freedom, and fear. To learn from all the possible lessons of duality that has been possible on Earth, you have experienced every different human aspect available on the planet. Today, many souls have now come to the end of their study of duality. Many of you have nothing more left to learn on Earth.
The major purpose of reincarnation is learning and also clearing “uncompleted” life lessons from previous lifetimes. After you master your lessons, you do not need to repeat them again. The number of experiences or reincarnated lives is completely a matter of choice for each soul. Some souls may experience hundreds of incarnations while others may master the same lesson in five incarnations.
Before you incarnate from the spirit world, a group of spiritual advisors helps you decide the lessons you need to experience in this lifetime. Between incarnations, all souls return to the “Spirit World”. Your spiritual advisors are known as your “Council of Elders”. The Council review and refine your spiritual lessons for your incarnation. This is known as your “Incarnational Contract,” which serves the purpose for each incarnation. Your contract also includes the need to teach and/or learn from other individual/s or groups of souls, thus you establish mutual contracts with others.
Situations and events are created to bring souls together to learn these lessons. Once the soul contract is finalized, you then select the secondary aspects such as the time and place of your birth, your parents, siblings, sexuality, health status, pets etc and then you finally incarnate into the body during gestation to begin a new incarnation. When you are born, you have amnesia (known as the Veil of Forgetfulness). You start your new life without any recollection of previous incarnations or lessons you have to master in this lifetime.
Each spiritual being has a different spiritual path. There is no right or wrong. Every good and bad experience gets you one step closer to perfection. Compassion means that no person has the right to judge another person’s decisions, choices, and wrongdoings, because you do not know what the spiritual lessons and/or karma those souls are here to experience.
Your spiritual development is dependent on your ability to consciously evaluate each human experience, understand lessons, accept the consequences of your actions and overcome your weaknesses, until you perfect your lessons. Else you will have to repeat the same script in your next lifetime.”
http://ascension2012.in/downloads/Ascension-Study-Guide.pdf