I would appreciate a more detailed explanation if you are minded to share it. Thanks.
In Keumgang, in terms of technique, a foot is lifted repeatedly, at times in a stationary pose (oreun hakdariseogi) and at times, as the start of a 90, 180, or 360 degree rotation. Regardless of the context, this lifting creates instability. This instability in the context of rotating on the axis of the standing leg permits more acceleration and the contribution of body mass (as opposed to only the contribution of limb mass) which in turn increases force at impact/completion (e.g., the most dramatic example being the foot stomp-juchumseogi-santeulmakki-kihap). So while there are many stable stances (juchumseogi) in Keumgang, they are repeatedly interspersed with much instability.
In Keumgang, in terms of philosophy, the most basic idea is that the repeated alternation between instability and stability may be considered to be symbolic of 1) the instability created by our clinging to desires/ignorance/delusions followed by the stability created by reaffirming our decisive release of desires/ignorance delusions or, more loosely, 2) the psychological instability we experience as we face a developmental dilemma prior to deciding on our action followed by the stability created by our taking of decisive action to resolve the developmental dilemma well.
Keumgang may be the first poomsae in which the role of instability in creating powerful physical impact (and in furthering human development) is recognized by a Taekwondo practitioner. When that is the case, Keumgang can serve as the impetus for recognizing the physical and philosophical importance of instability in other poomsae.
See pages 461-474 of the Kukkiwon Taekwondo Textbook (2006) for detailed descriptions of the physical techniques of Keumgang.
My thanks to Grandmaster Al Cole for extensive discussion regarding the physical and philosophical aspects of Keumgang.
Cynthia