Wu Ji and Taiji training will produce enough Yuan Qi to balance its power.

The first two stages of training, Wu Ji and Taiji, allow the practitioner to produce enough Yuan Qi to balance their internal power and improve their Qi quality, smooth the meridian channels and produce explosive power: Hun Yuan Jing. Once the practitioner has mastered these two stages they are ready to advance to the third stage to train Jing for use in application. This stage of training is called Push Hands. 

Through at least ten years of push hands training (single hand, double hand motion or static push hands), the practitioner trains to listen for Jing, yielding to Jing, and to emit Jing. You will be able to hear the opponent's intention at any moment, feeling your opponent's pathway of Qi, directing the opponent's Jing's landing point. This enables the practitioner to overcome motion from stillness. Softness overcomes hardness, applying four ounces to overcome a thousand pounds.

After practicing push hands to maturity, the practitioner can use Jing by subconscious free will. He can achieve a level of integration of hands, eyes, steady mind, body and footwork; and can apply it to Taiji freehand sparring. This is the advanced level of Taiji practice and requires over 20 years of practice. That is why we say that you don't know Taiji if you only have ten years experience. You know a little bit if you have 20 years experience. Only then can you say that you know Taiji. To learn Taiji push hands requires an experienced master instructor.