Any and every verse of the Bhagavad Gita is a mantra. Any and every verse of the Upanishads is a mantra. Any śloka or sākhi by the saint poets, when in the language of the masses, is a mantra. Nanak Sahib, Kabir Sahib say something—all of that is a mantra. Which means, there can be no single, common mantra for everybody, because the mind differs. All that differs is mind.
Because the mind differs, therefore the mantra that would be useful to the mind at a particular stage, at a particular time and place, would also be specific to that time and place and situation. Which means, you cannot have one mantra for an entire lifetime. Which means, you cannot have one mantra for an entire community. Which means that one mantra that is useful to you in the afternoon would not be so effective by the evening; by the evening, you might require another mantra.
The Truth cannot change; but the mantra must change.
