I love this quote and this is definitely something to meditate upon, and most certainly, when you are in an asana (posture).
One of my favourites to work with and meditate upon while practising is Warrior 2 or Virabhadrasana II.
To execute this posture, stand with the legs apart, at a distance that is comfortable for you. Ensure the feet are pointing straight forward and equal to each other. Then, turn the right foot out 90 degrees and push the left heel back 45 degrees. Try to ensure that the heel of the right foot is in line with the arch of the left.
Then, raise the arms in line with the shoulders and relax the shoulders down, keeping the arms strong. Turn the head to face the right arm and bend the right leg. At this point, it is important to make sure that the right knee is kept over the right ankle. This ensures that the correct muscles are being utilised, while protecting the knee and ankle joints. Further, you should be able to see the big toe of the right foot on the inside of the right knee. If the knee drops too far to the inside of the thigh or to the outside of the thigh, the correct muscles will not be engaged and the knee and ankle may take strain.
The left leg remains strong and the left hip pulled back – almost as if the hips are being pulled apart. To do this, tighten the buttocks. Meanwhile, the arms remain straight out. You may want to look behind you to ensure that the left arm is in line with the body and still at shoulder height.
Turn the head to face the front again (the right arm), and soften the gaze. Breathe into the abdomen or Solar Plexus Chakra. Focus on the energy within your body. Focus on each muscle. Starting from the feet, through the legs, the buttocks and hips, the abdominals and spinal muscles, the chest, arms (they should almost feel as if they are being pulled apart), the shoulders, hands and finally the head.
Breathe into the posture. Try to take ten breaths while holding this posture to begin with (remember, it is your body and if you feel tired, slowly come out of the posture).
If you are truly focusing on the posture, the mind should not wander to other areas of your life, but rather on and around the asana and your breath.
Become the Warrior.
To come out of the posture, straighten the right leg, turn the body to face the front, turn the feet in, lower the arms and walk the feet back into the centre. Remember to repeat the asana on the opposite side.
Before practising Yoga, you should ideally contact or work with a qualified Yoga Instructor.