Things often written for one subject, often exposes it’s universal nature.
Be as still as a mountain, Move like a mighty river.
Your motion should be rooted in the feet, released through the legs, controlled by the waist and manifested through the fingers.
The feet, legs and waist must act together simultaneously, so that while stepping forward or back the timing and position are correct.
If the timing or position are not correct, the body becomes disordered and the defect must be sought in the legs and waist.