Why exactly 1,25,000 chants? This is not a random number. In Vedic cosmology, we live in the Kali Yuga. The energy density of the atmosphere in Kali Yuga is dense and resistant to spiritual vibrations.
To break through this resistance and manifest a result in the material plane (Akash Tattva), a minimum acoustic pressure is required. The ancient Rishis calculated this threshold to be 1 Lakh mantras. However, human beings are prone to errors (pronunciation mistakes, loss of focus). Therefore, an extra 25% (25,000) is added as "buffer" or "interest" offering to the deity.
"Success in Mantra Sadhana depends on the saturation of the ether. Just as water boils only at 100°C, the result manifests only after the count crosses the critical mass of 1.25 Lakh."