If I may intervene, it might help both of you to understand that there is a difference between concentration "Dharana" style Japa mantra (i.e. repeating a mantra consecutively), and effortless sustaining of attention "Dhyana" style Ajapa Japa mantra (which is what TM is for example). One usually precedes the other in the Yoga Sutras of Patanjali.
Concentration on consecutively vocalising and then repeating words / phrases / mantras mentally (so Japa Mantra), whether devotional or not, but with a meaning and/or intent, does actually work to realise whatever is being affirmed (if believed), it's like "self-talk" in psychology and eventually impresses one's subconscious mind. That said "Dharana" will not get you to Samadhi i.e. even perfectly concentrated mantra repetition (that will just make you a robot) is only a step in the direction to "Dhyana" (effortless sustaining of attention on something) - which eventually will. The attention in "Dhyana" can be on many things really, a mantra, breath, a candle, even attention to the feeling of being relaxed.

"If meditation is not possible do Japa. Realisation will come through Japa" - Sri Sarada Devi

Anyway I hope I brokered the peace.