It's the mind through which we actuate our body and ultimately the world.Infact it is an interface between the soul & the body. Its a part of Nature,but very minute & extremely dynamic in action. We can't do any work without actuating the mind. Now if the mind is not filled with proper Sankalps (or thoughts) then it will work on the stray thoughts ,which already exist in its store. It is due to this fact that we have the phrase 'An idle mind is a devils workshop'.So to avoid this mind to act as a devil ,all the dharma's & the great men suggest the JAP with God's name. This will prevent any other stray thought to enter in to it. and the result will be a Harmonious and happy life So while we fill our mind with good Knowlege (GYAN) we can form the habit of doing Internal JAP . I for myself like to do this with, what Rishi Dayanand ji has given us, as Pranayam Mantra, which is as follows

" OM BHU, OM BHUWAH:, OM SWAHA:, OM MAHA:, OM JANAH:, OM TAPAH:, OM SATYAM:
Try this also while doing all the Pranayam, which we are doing these days.