Each of the powers or forces in the world has its own bija mantra, such as Aim for Saraswati, Shreem for Laxmi, Kleem, Kreem, Hreem and so on.
All the short, seemingly meaningless mantras which you might have heard, are called bija mantras.
Those bija mantras are just like little bombs, the type of time bomb which explodes just at the right moment. Just as you plant a seed in the earth and from that a giant tree grows up, giving thousands of fruits, such is the power of the bija mantra.
With the practice of anushthana – prolonged mantra repetition for a fixed period of time and number of malas, and regular sadhana, the power of the mantra is awakened. When that power is awakened, the consciousness takes the form of the mantra and then the real work of the mantra begins.
Please, remember one thing.
Shakti, energy, is not only of one type. It has innumerable forms.
Although the primal shakti, the root shakti, is one, its manifestations are endless.
That is why we worship Devi in so many different forms. The same principle is also found in science. When electricity is flowing from one central circuit, the amplifier, tape recorder and all the appliances are working. The same energy which gives heat from the heater, gives coolness from the fan.
These are the varied manifestations of one energy. The truth is that shakti is not just of one kind. Intellect is one shakti, memory is another shakti. Speech, prana, knowledge, are all shaktis, without which we cannot exist. So there are different bija mantras for the awakening of these different powers.
For example, take vidya shakti, the power of knowledge. It is in the form of Saraswati. I am not talking of the goddess Saraswati whose idol is worshipped in the temple, but I mean that energy, that shakti which is within us in the form of vidya or Saraswati. What is the way to awaken this energy? Of all the methods given, the best is to take the bija mantra of that shakti and to awaken its sleeping potential.
There are many other types of shaktis pertaining to the body, to disease, even to snake poison, and so on. In many diseases, if japa anushthana of Mrityunjaya mantra is perfomed, the power of the mantra is awakened internally, giving the desired result. By the practice of mantra japa, the aspirant's conscious will is awakened and through the willpower everything is accomplished.
Paramahamsa Swami Satyananda Saraswati