The word Mantra means something that we will ponder, that we will reflect upon.
That is, you go to a teacher,
they say something and I go back home and reflect upon that.
मननात् त्रायते इति मन्त्रः॥
mananāt trāyate iti mantraḥ ||
“Who reflects on this, will cross the obstacle”.
– Extract from an interview with TKV Desikachar on Vedic Chanting