Nimittam aprayojakam prakrtinam varanabhedah tu tatah ksetrikavat
nimittam incidental, instrumental, efficient cause, a pretext
aprayojakam not useful, of no use
prakrtinam of natural tendencies or potentialities
varanam covers, veils, obstacles
bhedah split, division, separation
tu but, on the contrary
tatah from that
ksetrikavat like a farmer, like a peasant
Commentary from Light on the Yoga Sutras by B.K.S. Iyengar
Nature’s efficient cause does not impel its potentialities into action, but helps to remove the obstacles to evolution, just as a farmer builds banks to irrigate his fields.
As a farmer builds dykes between fields to regulate the flow of water, evolved yogis channel the abundant flow of nature’s energy to free themselves from the bondage of their actions and develop spiritual insight. Even if sadhana (practice) fails to bring about complete transformation in the life of the sadhaka (practioner), it certainly serves to remove obstacles in the path of his evolution.
A farmer heaps up banks of earth to collect water and soak part of a field. When on area is soaked, he opens the bank to enable the water to flow into the adjoining area, continuing until the entire field is thoroughly irrigated. The he sows the best seeds to get the best of harvests, and enjoys the fruits.
Nature’s energy now flows abundantly in the sadhaka. This energy is built up and concentrated through the practice of asana, pranayama, and bandha, which can be though of as ‘dykes’ in the system to regulate and channel energy, so that mind and intelligence may diffuse evenly throughout one’s being.