Relaxed body

When you train your body to be relaxed you should be able to move freely
without tension in the joints and ligaments.
Your mind must also be relaxed and calm.

You should feel that you are floating but heavy at the same time;
connected to the ground but agile and flowing.

Your awareness with your surroundings and yourself should heighten
and a sense of being in the here and now.

You cannot force this feeling, you must train body and mind to relax.
The results will follow with continuous training.
Be patient.

Significance of yielding

One of the most difficult aspects of learning kung fu, is yielding or being soft.  On a very basic level, this means that your muscles are relaxed rather than tense and your joints mobile rather than being held in place. 

This is not just physical, your mind must yield also, be able to change and adapt to what is happening.  Your body must be mobile and loose. 

The transmission of energy from the ground through the body and out through the fingers can only be done if your muscles are relaxed and your joints and tendons are mobile.  If you lock any part of your body up by using tension then the energy will be impeded.