The key to doing good stance or zhan zhuang is firstly visualization, and secondly Jing [or Chi] exploration (聼勁 or 摸勁). In Embracing One, with palms facing down, the visualization is a force acting upwards (i.e with a practitioner's energy acting down to neutralize the upward force). In Holding Golden Urn, it is just the opposite. The result is that the shoulder joint will experience a feeling of flow (criterion of success: if you don't experience a feeling of shoulder flow, you probably does it wrongly).
Jing exploration in the two styles aims at opening the shoulders (and consequently the shoulder blades too) in two directions. The explorations (the nature of which is minute or nano movement) are led by the two thumbs, either bring them together towards the centre of the body or moving outwards to the two sides.
Are these two stances unique to tai-chi nei gung? No. In Wang XiangZhai's combat stances, there are similar stances (with 70/30 weight distribution as per combat stance Wang-style). The benefit of 24 styles is that the important objective of shoulder and shoulder blades opening has been singled out into two stances for more focused training.
|Mantak Chia doing Holding Golden Urn|