Mantra (मंत्र) means a self advise.
‘Mananat trayate iti mantrah‘ is how Mantra is defined in Sanskrit.
It means that by repetition (mananat) of which, you overcome/protected (trayate) [overcoming or protection from bondage/troubles/cycles of birth and death] is (iti) called Mantra.
The word Mantri (advisor/minister to king) is also derived from Mantra as his job was to advise and direct the King.
It is a sacred utterance, numinous sound, or a syllable, word, phonemes, or group of words set in an order to produce certain vibration in atmosphere, which gives the desired effect to the person who practices it with concentration.
There are many mantras like Narayana Ashtakshari, Siva Panchakshari, Gayatri Mantra etc and each mantra is very profound and carries immense amount of knowledge.
For example, Gayatri is defined as ‘gayantam trayate iti gayatri‘, which means the one who protects (trayate) the one who sings (gayantam) is (iti) gayatri.
Every mantra comes with the following fundamental aspects:
Rishi or Sage: Mantras are not created, rather they are revealed to the sage during deep blissful meditation when the prana ascends towards sahasrara chakra. That is why we touch the crown of the head while taking the rishi’s name. So the rishis are called mantra drashtas (the seers who ‘saw(drashta)‘ mantra; drashta comes from drishti(vision) ) rather than the mantra kartas (the makers).
Raga/Chandas or Melody/Meter: Chanting of the mantra is the most important of all and is about the sounds and the vibrations. So it comes with a meter or pitch. This is just like we have talams (adi, rupaka, etc) in classical music. The names of these meters are gayatri (its also the name of a meter), anushtup, trishtup, brihati, pangti, etc. They come with a distinctive time length for each cycle. For example the Bhagavad Gita is written in Anushtup, the Rig Veda is written in Gayatri meter, etc.
Devata or Deity: There is a presiding deity for every mantra on whom the devotee meditates on by keeping it in the heart chakra. That is why the heart region is touched while taking the name of the devata.
For Gayatri mantra , its the sun. All this has to be done with so much love (heart chakra = love), respect and innocence.
The way the entire agama is structured is just so beautiful. Even before this is done, the devotee does pranayama to get his mind centered and then with a lot of love and gratitude the mantra is taken. If there is no love and respect, the mantra does not bear any fruit.
For example : Sri Vishnusahasra Namam has these Rishi, Chandas and Devata
asya sri vishNoH sahara-nAma-stotra-mahA-mantrasya
sri veda-vyAso bhagavAn RishiH, anushtup Chandah,
sri mahA-vishNuH paramAtmA sriman-nArAyaNo devatA
Ancient seers knew the power of words very well and they structured them so wondefully. Each sound vibration from the mantra chanting enlivens a specific part of the human body. The rhythm and the dynamics of these sounds in the body are just phenomenal and very conducive for the mind to slip into meditation and go into total rest. The mantras have many more secrets hidden, for example, the 24 syllabus that the Gayatri is made of correspond to the 24 vertebraes of the spinal column, the namakam and chamakam carry ancient ayurvedic medicinal recipes that are used to cure diseases.
Lord Krishna himself stated in BhagavadGita that among vedas, he is Sama Veda.
This entire Sama Veda is dedicated to music and vibrations.
Modern Scientific Experiment on Science of Sound and Vibrations
An interesting modern day experiment on how our words influence our minds and even body structure was conducted by Dr. Emoto.
Different sounds of love, friendliness, etc were played out to water crystals as well sounds of negativity to a different set.
He found out that crystals with the positive words are so beautiful and well organized compared to the other set. If this can happen to water molecules, imagine how our own thoughts and the words we speak effect our bodies and environment.
Mantras used as weapons and for destruction or self-protection
Ancient vedic scripts are full of descriptions of weapons being called by mantra. For example, many weapons were invoked by mantra during the epic Kuruksetra War in Mahabharata.
Nuclear weapons like Brahmastra, Guided missiles like Vayuvyastra, Pasupatastra, Narayanastra etc were evoked and energized through mantras.
One Clinical Test of the Benefits of Mantra Chanting was performed on 3 groups of 62 subjects, males and females of average age 25.
They chanted the Hare Krishna Maha Mantra twenty-five minutes every day under strict clinical supervision.
Results showed that regular chanting of the Hare Krishna Maha Mantra (Hare Krishna Hare Krishna Krishna Krishna Hare Hare Hare Rama Hare Rama Rama Rama Hare) reduces Stress and depression and helps reduce bad habits & addictions. These results formed a PhD Thesis at Florida State University.
No wonder why Hare Krishna mantra is regarded as the best to control ill-effects of Kali Yuga (present epoch).
‘In a Disco, your Mind makes you Dance, In a silent meditation, you Make your Mind to Dance’