In Upasana one has to concentrate one s mind on a single object. This is not possible if one is standing or lying. The mind of a standing man is directed on maintaining the body in an erect position and therefore incapable of reflection on any subtle matter. A sitting person may easily avoid these several occurrences and is, therefore, in a position to carry on his meditation. The sitting posture contributes that composure of mind which is the sine qua non of meditation.
Meditation is to be practised in a sitting posture, as in that case only meditation is practicable.
And on account of meditation. An argument in support of Sutra 7 is adduced. Further, such continuity of thought is Dhyana or meditation. It can come only when the limbs are not active and the mind is calm. Concentration being an uninterrupted and unintermittent current of thought sent towards a particular object, the sitting posture becomes indispensable.