Since Louis did not translate the excerpt he quoted, let me give it a shot.
‘´›‰¿˜rœk—eˆÕŒ`¬Žè¨™K‰», ˆöŸœä’ˆÓ gŒÛ˜rh. ŒÛ‹N˜rŽqŽgŽè¨é “î•½’¼.
"As a matter of fact, in seating the wrists, it is easy for the shaping of the hand position to become rigid. Because of this, one must pay attention to activating the wrists. Moving to activate the wrists makes the hand shape/gesture soft, spongy, even and straight."
I think I might understand the reasoning behind this statement, but generally approach this problem from a slightly different direction, based on what I understand from the teaching in the Association. For most people, I do not think the solution lies in imagining or cultivating any type of feelings in the wrist in isolation. Although I think this can be done successfully, I think this instruction can be very misleading and lead people to ignore the physical and try for an exclusively mental or metaphysical solution that will prove illusive.
What I understand to be important is to understand that seating the wrist involves a Taiji relationship between extending the Jin point in the palm or palm heel and preserving the Jin flow from the spine to the Jin point. From shoulder to palm (heel) you want a straight line of energy, but you cannot make the arm too straight. You want a curve that tends toward straight. Seek the straight in the curve (and vice versa).
If you do not extend the fingers enough, you do not draw out the Jin point. If you extend them too much, you choke off the Jin flow. If you bend the wrist too much, you destroy the smooth curve and cut off the Jin flow. If you do not bend the wrist enough, you hide the Jin point. If you bend the elbow too much, you destroy the straightness and extension of the Jin flow. If you do not bend enough, you destroy the curve and cut off the flow of Jin. How straight the straightness should be and how curved the curve should be depends on the application.
What I do is to think about extending through the Jin point in the palm or palm heel, helping with the fingers, but feel for the curve extending from the Jin point through my arm to my elbow and to the middle of my back between the shoulder blades. The curve is like an arch. If the curve is right, the arch will be strong and the Jin will be strong. If the Jin point is drawn out and exposed, I know that I will be able to send it out. The more I need extension, the flatter the arch will be (e.g., in the final position of Push or Apparent Closure) . The more I need to store or absorb energy, the more rounded the arch will be (e.g., the position in Push or Apparent Closure when the hands are near your body or the final position of the top arm in Fair Lady Works the Shuttles). In some transitions, you need a temporary double arch, joined at the elbow, such as when the seated palm is tucked near the arm pit in Brush Knee and Repulse Monkey.
If you think of bending the wrist as only an isolated, local movement, I think the tendency will always be to make a shape that is stiff, weak, and brittle. If, on the other hand, you activate the relationship of the wrist to the entire curved line linking the middle of the upper back and the tips of the fingers, you can form something that feels alive, flexible, yielding, and yet strong.