Being cheerful can open our hearts to stillness. But what does that mean to transition from cheerfully doing to standing still? How do you know when it’s time to step back and wait “with utmost assurance” for God to reveal his arm? I think it depends a bit on what kind of “doing” needs “stilling.”
To “do all that lies in your power” could be interpreted in at least two ways: 1) having done all you can and recognizing you have exhausted your options, and 2) doing all that lies in your power and feeling you still haven’t done enough.
Having Done All You Can
The first is that you have done everything you can, and you’re out of options. You are sick, for example, and you have seen all the doctors, tried all the natural remedies, asked for 
blessings, changed your diet, and so forth. Another example might be that you have applied to college or graduate school and are just waiting to hear back. Or you’ve done your best to counsel a child or a friend and now it’s up to them to move forward, or any number of situations where you feel at a loss to do more. Your call to stillness is to trust, and to say, I did my part, now “thy will be done.”
In Ecclesiastes, there is a poetic scripture about accepting what comes next, and trusting in God’s hand over all. It reads:
Cast thy bread upon the waters: for thou shalt find it after many days. . . .
If the clouds be full of rain, they empty themselves upon the earth: and if the tree fall toward the south, or toward the north, in the place where the tree falleth, there it shall be.
[She] that observeth the wind shall not sow; and [she] that regardeth the clouds shall not reap.
As thou knowest not what is the way of the spirit, nor how the bones do grow in the womb of her that is with child: even so thou knowest not the works of God who maketh all.
It will rain when the clouds are full. Trees will fall one way or another, and that’s where they’ll stay. You don’t understand how things work. You don’t even begin to comprehend how a child grows in your own belly. But God maketh all, and he does understand. So choose to trust. Cheerfully do what you can, and then let go. The first line in the scripture above is, “Cast thy bread upon the waters: for thou shalt find it after many days.” I think of that image as casting our need to understand—our need to know why things are as they are—on the waters and letting it float away. After many days, it says, we will find it again—perhaps when we are able to understand better and accept it.
Doing All That Lies in Your Power
A second interpretation of “cheerfully do all that lies in our power” may speak to those of us who feel overwhelmed—to the woman who says she is literally doing all that lies in her power, and it is too much, and there is still more to do. In that case, I think the message we should take from this scripture is that God is aware of our limits, and he is telling us to stop —to allow Him to do his part. He’s encouraging us to realize that if we don’t have time or space to practice stillness, we aren’t trusting Him enough. Elder Richard L. Evans said, “There seems to be little evidence that the Creator of the universe was ever in a hurry. Everywhere, on this bounteous and beautiful earth, and to the farthest reaches of the firmament, there is evidence of patient purpose and planning and working and waiting” (Conference Report, Oct. 1952, p. 95).
This is hard for me. My favorite scripture is “Fear not to do good,” for heaven’s sake. I try hard not to let fear get in the way of extending myself. But there is a tension between doing all that lies in my power, and stopping to stand still. It is our individual privilege to find the right balance for each of us, but I submit to you that making deliberate choices to be cheerful, and thoughtful choices to step back, to meditate, to pray, and to trust will open the door for God to steady and direct your ship. This poem by the great American poet, Lucille Clifton, captures this for me:
blessing the boats at St. Mary’s
may the tide
that is entering even now
the lip of our understanding
carry you out
beyond the face of fear
may you kiss
the wind then turn from it
certain that it will
love your back may you
open your eyes to water
water waving forever
and may you in your innocence
sail through this to that
Do what you can. Do it cheerfully. Trust God to take care of the rest.