It is important to remember that in dynamic holistic terms, union (1) and nothingness i.e. emptiness (0) are fully interchangeable.
It may be helpful to view ultimate union in structural terms as the perfection of form i.e. where the opposite polarities of form fully coincide.
So pure union in this sense can be represented holistically in structural terms as 1 - 1 i.e. where the positive direction of form is fully balanced by its negative.
However 1 - 1 in holistic (as in analytic terms) = 0.
So therefore from this alternative perspective, what is ultimate union (as regards the structures of form) equally represents a dynamic state of (creative) nothingness (i.e. emptiness).
So ultimately form and emptiness (structures and states) are identical as pure Spirit.
However at the level of phenomenal recognition (regardless of how well defined), structures and states separate to a degree in experience and both dynamically interpenetrate with each other.
So from a proper experiential viewpoint, it is vital to maintain proper balance as between both perspectives.
As a general criticism, I would believe that in most esoteric spiritual traditions - especially Eastern) undue emphasis is given to states (over structures) with ultimate reality being viewed in an unduly contemplative manner.
This then can impede proper emphasis on the corresponding need for mature active involvement in the world of form (through immersion in practical affairs).
As with a fire for the flames to keep burning we must keep feeding it with material fuel. Likewise for the flames of contemplation to keep burning we must feed it with committed active involvement in the world of form.