The universe is made from sound, and sound is the basic and main source of energy. Every being has energy. It transcends from one form to another. Similarly, each being has a sound of its own. That’s how we can tell the sound of glass from the sound of metal or wood or water. Sanskrit is the most evolved and ancient language in the world. It actually has 46 alphabets denoting a sound each. When these alphabets form words and then mantras, it is energy coming together to form a force that has the power to change and manifest.
As sound is of the nature of the syllables composing it, the tantra affirms that the creative force of the universe resides in all the letters of the alphabet. The different letters symbolize the different functions of that creative force, and their totality is designated as matrika or the "mother in essence".
Thus the mantras and shlokas are not just mere combinations of whimsical sounds but the subtle form of the presiding energy; and hence the technique of reciting these mantras is to create the force required to connect and communicate with the energy, of that particular mantra.
It is not only mantras or shlokas, but even our classical music, is a form of potent energy. That is why it has the power to cause rain and light lamps.
Even in our daily communication, our tone is more important that our words. How we say things is more important that what we say. It is the pitch, the rise and fall, the stretch, in our tone that decides the response we get. Responses are seen, but on a deeper level, it is our psyche, and the auras around us that get influenced by the tone and lead us to respond the way we do.