Sri Chinmoy: It depends on the individual. If an individual is a beginner, it is advisable for him to sit in the lotus position or in a similar upright position. I tell my students to try and sit in a comfortable position but to keep their backs straight. When the spinal column is straight, one can breathe properly. So long as we keep our back erect and feel that we can breathe properly, we do not have to go through any austere postures. Certainly, if the lotus position is painful or uncomfortable, you should not use it.
Now, it is not only the physical posture that counts, but how pure we are in our thoughts. No matter how well we do our lotus position, we cannot make any progress in our meditation if our minds roam uncontrollably and we become victims to unpleasant and undivine thoughts. Certainly it does help to some extent if we can sit in the lotus position, but real meditation comes only when we know how to silence the mind and open the heart. When we silence the mind and open the heart, God can enter into us with His Peace, Light and Truth.