Mantras, which are wrongly described as a thing which is religious and/or is a thing of a particular religion whereas the fact of the matter is, mantras are the aids and tools which establish the link of the life energies to connect with the cosmic energies in particular way that too in order to achieve and/or to have something happening in one's life (there are mantras which are capable of even changing the things for many number of individuals too, at one time, for which other elements like fire, earth, water, ether, space are also engaged, this process is known as "Hawan").
It is a scientific thing, the effects generated by reciting mantras can also be evaluated (to an extent) by using more machines, like sonography, EEG etc and are not a thing of just blind faith or even faith, these mantras when recited with due diligence (utmost focus and concentration and there is prescribed control on inhaling and exhaling. These are not prerequisites but are just norms and regulations, which can be easily understood by using this example, as the things which a physician advises to be done in addition to having medicines. The recitation of the mantra, as to how many times it should be recited is governed as to what is the difference the gap between the energy energy required to achieve the thing and the prevailing energy levels (of that particular kind), which a profound master would analyze and suggest its pupil accordingly, as is the case in any medicine or thing which will change the chemical composition within, like when you visit a doctor for say fever then the doctor wont prescribe the same medicine for all the patients suffering with fever, every individual patient has to be examined and evaluated and the reason for fever has to be identified its post all this that medicine is prescribed, self medication is always fatal likewise if recitation of the mantra or even the choice of which is done by just choice or liking or by reading it on Google or someone else got benefitted or is doing would definitely be wrong way to approach. The recitation of the mantras is not a thing which can be associated with Bhakti (unconditional love approach towards almighty), rather mantras when recited generate and enhance a particular energy within, which is meant for the life energies to achieve something, they are tools and should be extended their due respect.
There are two kinds of mantras in general one are the beej (a sanskrit word which in english language can be translated as seed, from where the things germinate) mantras and the mantras which are combination of words and beej. Beej mantras are the mantras which are found in the vedas (the primal and the oldest scriptures) and the other mantras are the mantras which have been developed by sages over the course of time to meet the requirements and needs of the changing society, with the evolving structures of the socities the needs of the individuals changed, like the kind of physical, mental, emotional and psychological ailments which this modern society people would be enduring would not have existed at those times, that doesnt mean or should not be taken as those mantras are obsolete, the triggering point and the energy point and the energy responsible remains constant and same its just there is new manifeststion when it's imbalanced, again reteriating the innuendo of mantras, their recitation should only be adopted post analysis done by a profound master.