The Reason Why We Came Down To This World
Every soul comes from under the heavenly throne. The soul says to G-D we want to enter Garden of Eden. G-D says you don't have the clothing to enter. You will be embarrassed sitting there with out clothing.
The soul asks, " How do we get the clothing"?
G-D says by going down to the world and performing Mitzvot. Every time you perform a mitzvah, that limb of your body in which you did it with gets clothed. After performing all the Mitzvot, you will now have all the clothing needed to enter Gan Eden. The final resting place where the soul has eternal tranquility and peace.
In many cases, the soul does not want to risk it, by coming down to this world. Since the Soul is afraid of all the distractions and tests, and will end up not fulfilling it's mission. However G-D forces it to come to this world. So the soul can ultimately enter Garden of Eden. The soul begs make me lamb, blind or autistic so I do not sin. Pending on the mission of that soul G-D will do accordingly.
The highest form of soul there is, the soul which comes down fully functional and is able to perform all the commandments. The person who performs all the Mitzvot will be able to enter Garden of Eden and be fully clothed. If he is missing Mitzvot or has sinned. He needs to be cleansed or he will have an eternal handicap and forever be embarrassed. Therefore G-D in his merciful way, gives the soul another chance to come back down to this world. Thereby rectifying the mistakes so he can go to his final resting spot.
Unfortunately, when one sees a child under the age of 13 dying. It's tragic! However this child came to rectify its mistakes and right after awaits anxiously to return its soul. The souls does not want to be on this world longer then it has to. Since it may come to sin again.
There was a child who died at 2 years of age. The parents could not come to terms with their loss. One night the child comes to the mother in a dream and says
" Mother stop crying. The mother asks, why did you leave me. The child responds. In my past life. My parents became observant after I was 2 years old. But until then, they ate non-kosher food. As a result I was fed unkosher food through my mothers milk. I needed to come back and rectify the time and food I ate while I was an infant. G-D picked you as my parents since you are very special and observant. G-D trusted you that you would make sure I am fed only kosher food. Thereafter accomplishing my purpose for coming down to this world.
If we take it upon ourselves to do good deeds on behalf of the deceased, we can rectify their mistakes and they would not have come back to fix anything. Since the process is Painful and not all the time do they accomplish their mission.