...I'm no Dalai Lama.
In Buddhism, you must strive to do good deeds in order to accumulate "Good" Karma, to counteract all the "Bad" Karma that we ALL have accumulated over the course of Hundreds of thousands of life times. And, the more "Bad" Karma you have, the lower the Life form you take.
The Human form is the highest physical form, and it takes thousands of lifetimes as lower forms (dogs, cats, rabbits, bugs, snails, worms, etc.)for your Consciousness (other religions call it Soul, Spirit, "life force")to reach the Human form. The lower you go, the more you suffer (non domestic animals are always looking for food and shelter), but, the more you suffer, the more "Bad Karma" you rid yourself of.
SO, eventually, when you reach the Human form, if you are lucky, you will be born Poor (I know this sounds wack, but hold on). If you are born poor, you are less likely to screw up, by being mean, and doing selfish things, that accumulate a LOT more "Bad" Karma that will send you back down to an animal form, or even worse, send you down to be a "Hungry Ghost" or to the level of Hell.
Here: this article explains it better than I can. If you have a few minutes, read the first six paragraphs.
Ever wonder it Buddhist had a "10 Commandments?" Well we call them the "10 the non-virtuous actions" that must be avoided. They are: killing, stealing, sexual misconduct, lying, slander, harsh speech, idle gossip, covetousness, harmful intent and (holding)wrong view(s).
..."The backbone of Buddhism is the theory of karma and rebirth, the law of cause and effect. Buddhists believe not in a creator, but in beings fashioning their destiny by their own actions. In the course of their lifetime, living creatures perform virtuous or non-virtuous actions (karma) which create predispositions for rebirth in any of the six realms of cyclic existence. Virtuous actions bring about pleasant rebirths in the upper realms of gods, demi-gods and men and non-virtuous deeds, suffering and rebirth in the animal, hungry ghost and hell-beings' realms. When beings have exhausted the karma which caused their rebirth in a particular realm, in dependence on other accumulated karma, they take rebirth in another realm, wandering endlessly within the limits of cyclic existence until they find a way out to liberation or the state of Buddhahood- the ultimate goal of Buddhist practice.
Among all the creatures of the six realms, humans are the most fortunate, and have the best opportunity for attaining the ultimate achievement. Gods and demi-gods dwell in immeasurable happiness, exhausting the fruits of their positive karma, and are too distracted with worldly pleasure to seek liberation from cyclic existence. Hungry ghosts and hell beings are too disturbed with suffering and animals are too dumb. Humans, who enjoy both pleasure and pain are the only ones who can seek liberation.
The driving force of this aim for the attainment of Buddhahood is motivation, of which there are three types; motivation of beings of small, middling and great capacities. Though the ultimate goal of all three is happiness and freedom from suffering, the extent of their goals is immeasurably different. The being of smaller capacity's virtuous acts are aimed at securing a rebirth away from the hells, and his basic rule of conduct for achieving this is avoiding the non-virtuous actions which bring about lower rebirths. These are: killing, stealing, sexual misconduct, lying, slander, harsh speech, idle gossip, covetousness, harmful intent and wrong view.
The being of middling capacity seeks to go one step further and achieve liberation from cyclic existence by realizing the Four Noble Truths: true sufferings, which are like an illness, sources, the internal and external conditions that bring about that illness, cessations, the state of being curedo the illness and paths, the medicine which brings about the cure. In order to realize these Four Noble Truths, one must realize
1) the suffering of cyclic existence, like a sick person identifying his ailment,
2) that the origin of suffering is karma and defilements, like a patient identifying the cause of his illness,
3) the existence of a remedy to suffering, like a patient knowing that his illness can be cured,
4) that engaging in the paths will bring about freedom from suffering, like a patient realizing the benefit of medicine..."
(more at link)
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http://www.tibet.com/Eco/eco8.html>