Mantras are not a necessity in meditation – they are but one of many tools – but we do need a definite sustained practice to focus and stabilize the mind somewhat. I say somewhat because you don’t want the willful component of your meditation to be too tense. The classic metaphor is that of the moderately tense strings of an instrument.
You will need an anchor to come back to when the mind wanders or scatters as it inevitably will. A mantra is just such an anchor, like the breath, an image, a point in the body, etc. These are classic entry meditation objects.
On the other hand you are not doing a concentration for its own sake: your purpose in meditation should be clear in order to guide yourself through the process.
I suggest that one wants to incite and let its whole being synchronize and harmonize itself in order to sustain spiritual healing and transformative insight.
The efficacy of mantra is that it uses the energy of the voice directly to “shatter the chatter”, while other techniques rather take awareness away from the verbal realm into the perceptual field.
At one point the mantra gains an almost independent momentum, the mantra recites itself, and one is left to observe the outer and inner world with an accrued detachment.
Eventually you will be able to rest naturally in the mind’s openness, serenity and clarity of knowingness without reference points. But that’s a long way ahead… and until this ideal limit point, every faculty and every single event will be brought to the fire of consciousness.
Meditation is a voyage of exploration and it should stay enjoyable. Ease is of the essence: when the going gets tough one will find that hardships carry much less suffering when they are lived through in full awareness, and that even pain can be meaningful!