对拉 (Pulling in Opposite Directions) Sun Style

Recently, while we were performing our Sun style routine, my teacher came up to us and told us about this 对啦：Pulling in opposite directions.

He demonstrated this with Playing the Lute(手挥琵琶 ) where, as he moves his left hand forward, and his right hand backward, his back area actually seems to be moving backward, centralising his body. Next, when he does the Block Parry and Punch(搬拦捶) this is also shown. He says it is the pulling in opposite phenomenon in taichi.

According to him, the benefits of this pulling action is:

1. Stablises the person
2. Keeps you with rounded shoulders and in the Contain your chest, Stretch your back (含胸拔背) position.
3. Gives you a better structure, be it for defense or attack purposes.

Actually, he says this is applicable not only for Sun style, but througout all taichi styles. But as you can see from how I am writing this post, I don't really get the whole idea of what he is saying. So those who know, please enlighten me, and those who don't, food for thought!