What is the use of Japa(continuous repetition of a mantra.? Is it a good method to repeat words like “Silence” and “Peace” in order to establish silence and peace in oneself when one sits down to meditate?
A mere repetition of words cannot have much effect.
There are classical or traditional Japas which are intended to subdue the lower mind and establish a connection with higher forces or with deities. These Japas must be given by the Guru, who at the same time infuses them with the power of realisation. They are useful only for those who want to do an intensive yoga and spend five or six hours a day in yogic practices.
Japa such as you describe it cannot have much effect except to create a tamasic dullness, which should not be mistaken for mental silence.
Ref : Some Answers from The Mother