In plain words
The passing of stool and urine, cleaning the teeth, bathing and the like: because of these, in certain places the particles that breed disease multiply greatly. Everywhere there crores of particles arise, enter those who move about in those places and wear down their health. Filthy places like these, places where foul water flows, are the very home where ill health is born.
To keep these particles in check, in olden times they laid down five kinds of bath. The first, the mṛttikā-snāna. If you smear clay all over the body and then bathe, all the atoms are destroyed by that very means and the body becomes pure. It was for this that the prayer “O Earth, take away my sin” also came into being. The second: the ātapa-snāna; this they call the sun bath. It spreads the sun's rays over every part of the body; the light of the sun helps greatly to destroy the vicious particles. The third: the vāri-snāna (with water): both the particles that have settled on the outside and those that arise within disappear when you bathe in holy waters in a spirit of Bhakti. The fourth: the vāyu-snāna: a cool breeze blowing over the body helps the particles to perish. The fifth: the nagna-snāna: the ṛṣis taught that if you rub vibhūti over the whole body, through that very vibhūti the particles that spoil health fall away, and health is kept safe.
In ancient times the ṛṣis kept to cleanliness and bathed properly every day! The educated people of today mock this as uncivilised; the ancients, whenever anyone touched them, whenever they touched anything, would bathe and so win cleanness of body and Śānti of mind! The custom called “maḍi”, too, is a karma done for the sake of health and nothing else. When the moderns mock these people, those who stand for cleanliness unfortunately prove unable to answer them and uphold it. They too keep maḍi merely in outward things and nowhere else; but what its purpose is, what its fruit is, what the right way to observe it is: these they are unable to settle! Yet the customs of our forefathers were not without an inner meaning. To live as long as a man's full span of life runs, and to have the chance to fulfil all their hopes and aims: that was their one wish! They were firmly convinced that if you follow a good path in food and habits, life lengthens, and Śānti and happiness come to you. So that a man might not fall into dependence on others, might spend his whole lifetime in comfort, happiness and contentment, and might meet death without struggle, the ṛṣis laid down a measured diet and a measured way of living. The gross part of what is in food is passed out as waste; its subtle part turns into flesh, muscle, blood and other such substances. The subtlest of all, the causal part, shapes the mind and decides the good and bad in our feelings.