I stumbled across this piece today and it fit right into place.
Now note, you who know the conflict, you who know the fury of the oppressor, the bitterness of the animus of the devil, remember that the Lord allows him to go a long way in order that there might be this double issue. Firstly, an entering into the knowledge of the exceeding greatness of God's power – but how exceeding great must be God's power if against the mighty host of Assyria one angel alone is all that is necessary! To discover the exceeding greatness of God's power on the one hand, and on the other hand, through the work of the enemy himself, to drive the roots down. The Lord uses the adversary in his own hatred and bitterness to get our roots in, and to make us impervious to the Devil. He uses the adversary against himself in our trials. Roots downward, fruit upward. I am sure that is what the Lord is doing.
We are passing through deep experiences, the enemy is doing it and the Lord is not preventing him, but we are coming to a fuller knowledge of the power of our God and a deeper rooting beyond all previous shakeableness. And the Lord is seeking to have a people who cannot be shaken, against whom hell with all its demonstration of arrogance and pride, is impotent. "And the remnant... shall again take root downward." That is what the Lord needs.
From: Rooted and Grounded by T. Austin-Sparks
When the Lord is done with us, we will not be shaken or moved.