UP/Yoga/Zazen/Dhjana, etc. = letting everything go as the Universe wants (so called "God's will" :). Let  everything go completely as It wants!

Complete denial/ negation of the Self (everything that it wants). The negation includes "UP" (the idea of it)!

That means it is best "done" by silence and stillness. 

In (functional or non-functional) work it may not be possible. It's because the horizontal conflict  (the illusory product of thought that is the split into the subject and object) may be necessary  to perform it (operate on the so called objects of the "environment"). That is why whatever "we" "do" is so often the cause of so much stress, fear, effort, conflict, anguish, etc. The horizontal conflict is the root of it, the root of stress.

Meister Eckhart was a great Giant! (you can substitute "The Universe", "Void" or "Sunya" for "God" and "the world of the human society - all products of thought" for "creatures" in the passage):

"If therefore you want to have and find full joy and consolation in God, see to it that you are stripped of all creatures, of all consolation from creatures. For certainly, as long as creatures comfort you, you will never find true comfort. But if nothing can comfort you save God, truly God will console you, and with him and in him all that is delight. If you are consoled by what is not God, you will have comfort neither here nor there. If however creatures do not console you and you don't enjoy them, you will find comfort both here and there"

Regarding the so called "Will of God" :), the so called "religious" people might have not understood that war is also "the will of God" (the will of the Universe). Very simply because war is obviously currently happening, that is all the "reason" behind it why it's the "Will of God" currently. The thought of the people has obviously always have thought that "God" is some "being" somewhere (in "Heavens" :) who can choose and control what's going on in the world (what a funtastic product of thought! :) because of their catholic upbringing and all the conditioning in the society. But "God" (The Universe, Sunyata, Void, etc.) is simply THAT what IS (all of It, the whole unitary movement) that is happening. It does not mean that we - the monks.. should participate in war, it's an activity of the fools.. The task of the monks is stillness and silence. 

Suffering is the expression of the imaginary product of thought called the Self. Stillness and silence is the expression of understanding.