We have often heard of a proverb "You must reap what you have sown"... We are not really aware of wisdom and sagacity of that saying... It's not only that we are going to reap what we have sown in this life, but we will also have to "pay" for the things that we have done before, so we have to be very careful how we act... Human being's life is a great responsibility, but most of the people don't understand that and they are trying to act by their own caprice...
Karma is the cosmic principle of actions and reactions. Depending on the way we are acting we will get different reactions. Under the control of karma we, the spiritual souls, collect good or bad results depending on every act that we do in material world.
Karmic reactions include things and situations which are happening to us, but also the influence on our health, well-being, intelligence, physical shape, social status as well as on our personality and liking. When we have the liberty of action, our decisions are actually conditioned by our nature or personality which is developed depending on our previous actions. For example; good decisions make us good persons which take further good decisions. The principle of karma begins to affect when we start to enjoy separately from God, in other words when we live atheistic life. That kind of acting "locks us up" in continual circle and it is almost impossible to come out from it. Each action causes reaction which causes another action and so on with no end visible. Although reactions are good or bad, we still have to accept new bodies over and over again so that those reactions can be „charged“. In each life in this material world we have to suffer unavoidably because of our wishes, oldness, illness and death.
The Vedas gives us instructions how to insure good reactions or even better, how to get rid of this vicious circle... They tell us that spiritual actions are really the only efficient way of action because spiritual actions insure us freedom from the chains of karma. Spiritual action is the action in God's service and it's the essence of bhakti yoga. It awakes our love for Krishna by destroying our desire to enjoy separately from Him what is the root of our karmic bands.
Human life is intended for spiritual realisation and for receiving the freedom from the circle of birth and death. No other body except human body gives us this opportunity. No other body has such a high level of intelligence and consciousness... Therefore let's embrace spirituality as much as possible so that we can benefit from this opportunity which we got by being born in human body.