After the initial enthusiasm for chanting the Holy Name, gradually the mind becomes familiar with the Maha mantra and we tend to become mechanical with our Japa. The mind gets used to hearing the 16 words and after some time we are basically going through the motions of chanting to finish our quota.
Sound familiar? It certainly does to me.... and it's something the mind is always keen to slip into, - chanting for the sake of chanting and not really striving for quality and attention.
So now is the time to pull our socks up and take control of the mind during Japa...pronounce each word clearly, hear very carefully and keep the mind focused on the Holy Name.