What is the use of mantra japa if it’s really difficult to attain siddhi of any mantra for physical interaction or getting any wish fulfilled by god. If materialism doesn’t matter in our lives, what is the meaning of the present materialistic existence of humanity.
Firstly, it is as difficult to attain parmatma (God) as much difficult it is to realise the true self. As the true self is God from the very beginning. Realising this is attainment of moksh. Choosing how to realise it is a path of your deciding. One may realise it by chanting mantras, other might realise it by studying hard sciences. Someone else might do the same doing mundane chores throughout the day. As to which path to achieve realisation, is right or wrong, is totally a silly question to ask.
Coming to the meaning of life. I assume you are asking meaning of this current life. Technically, its meaningless, as, if not in this one, you may attain realisation in the next one. Then if there is no meaning, that means life is purposeless? No... Not at all. Purpose of life are 4 fold. Follow dharm, attain arthic stability. Follow Kam to enjoy pleasures. And lastly moksh.