Internal and external purification, contentment, mortification, study, and worship of God are the Niyamas.
In plain words: The Niyamas are five personal habits: keeping the body and mind clean, being content, self-discipline, study, and devotion to God. The teacher says inner purity matters most, but outer cleanliness is needed too.
External purification is keeping the body pure; a dirty man will never be a Yogi. There must be internal purification also. That is obtained by the virtues named in I.33. Of course, internal purity is of greater value than external, but both are necessary, and external purity, without internal, is of no good.
Namaste.
A calm guide to life, the mind and the old teachings.