He does better than that! By making the transformation a process rather than an event, we are able to watch the transformation take place, from glory to glory. It's especially delightful to watch it take place in the life of a loved one.

Also:

He uses the "foolishness" of the gospel to shame the wisdom of men; weakness to nullify the strong; and humility to break the back of pride (see 1st Corinthians 1:18-2:16). We remain in the world and subject to the planetary curse, groaning as we wait eagerly for the redemption of our bodies (Romans 8:23) from this weakness - yet all the while God is using that weakness and our longing for Him to bring many others to Himself, to multiply judgement against the wicked, and to demonstrate His mercy and power and justice to the whole creation.

Our suffering is temporary - barely a vapor - but what power it has upon others! Yes, God could snap His fingers and completely sanctify us in an instant. But using frail, weak mortal children to shame and to nullify the principalities and powers of darkness is so much more to His glory!

It's like the three Hebrew children in the fiery furnace. Sure, God could have prevented them from being betrayed, captured, bound, and tossed into a fiery furnace! But how much more incredibly awesome, how much more effective a demonstration of His power and love for His own, to accompany them through the ordeal so that they could emerge without even the smell of smoke in their clothing! Three children survived the worst that could be thrown at them. A tyrant was humbled by the obedience of three slave kids!

Sure beats just snapping His fingers. Our battle with sin and its damage is the same way.