Niyamas help us in purification of anthakaran. Tapas is utmost needed in every walk of life. With Tapas alone one can achieve whatever one wishes.
Tapa or penance is of three types -body, mind and speech as given in the Bhagavadgita XVII, Chapter Shloka 14 to 16
Physical Tapa – Worship of Gods-Goddesses and respect for elders and the learned, cleanliness of body, Straightforwardness, Ahimsa and Brahmacharya.
Tapa of Speech: speech that is without irritation, truthful, endearing, beneficial and also speech that reflects study and practice.
Tapa of Mind: Pleasant, gentle, non-reactive, with self-control and a positive perspective of everyone and everything.
The literal meaning of Tapa is to heat. The heating of and striving for purification of body, mind and speech should be consistently practised. Only then can the impurities be removed. It is also very important for living in harmony with Samashti, for the service of the society.
Tapa in simple terms would mean readiness to undergo pain to develop body, mind and intellect. Unless the body, mind and intellect are subjected to discipline these would not develop capability to undergo the rigours of the Yoga way of life. For example muscles develop only when subjected to the pain of stretching and weight-lifting and not allowed to be in comfort. For self-development, Tapa has become essential in today's life of comfort and over-indulgence.
Complete practice of Tapa or penance destroys impurity and enhances the powers of the organs and body and mind.