A balanced posture generates alert awareness

A balanced posture requires very little effort to sustain and allows the major muscles of the body to relax. This relatively small expenditure of energy, coupled with the phenomenon of relaxation, produces a distinct feeling tone of softness, ease, and vibratory flow. It also generates a natural condition of alert awareness. This dual condition of comfort in the body and relaxed alertness in the mind is the fruit of balance.

Will Johnson in "The posture of Meditation" page 20

Be alert

Be alert to all your thoughts and feelings, don't let one feeling or thought slip by without being aware of it and absorbing all its content. Absorbing is not the word, but seeing the whole content of the thought-feeling. It is like entering a room and seeing the whole content of the room at once, its atmosphere and its spaces. To see and be aware of one's thoughts makes one immensly sensitive, pliable, alert. Don't condem or judge but be very alert. Out of seperation, out of the dross comes pure gold.

J. Krishnamurti "Letters to a Young Friend" Page 9