Habakkuk 1

“Look among the nations and watch—
Be utterly astounded!
For I will work a work in your days
Which you would not believe, though it were told you." v.5

Read chapter 1
Habakkuk starts off his book with a cry out to the Lord for the sin of the people.  He's wondering why hasn't God acted or answered his prayer.  So God speaks up and says, "Hey just watch and see I'm acting and answering your prayer in a way that's going to astound you" (my paraphrase).  God's answer isn't talking about bringing the kingdom in but is talking about His justice coming to confront and set straight  their sin.  He was raising up the Chaldeans (Babylonians) who at the time were a small nation unknown to Habakkuk.  They were a corrupt people yet God was still going to use them as His instruments to carry out His justice.  Sometimes the answer to our prayers is that God lets things to get worse.  It may not be the way we want God to answer our prayers but He's the one writing the script, not us.  Bible teacher Nancy DeMoss Walgamuth says, "We cry, and we whine, and we fret, and we stress, and we struggle, and we wrestle with God. But know that God sometimes answers our prayers in the very ways that we’re resisting."  
The apostle Paul also uses this statement in Acts. 13:41 of a work which you will by no means believe, though one were to declare it to you.  Paul is saying this preaching about Jesus Christ and the kingdom about to come, surly when the Kingdom does come it it will be so amazing and mind boggling that many don't believe even though they have heard about it.
What is something God has said in His word that you don't believe?  How have you seen God work in your or someone else's life that was unimaginable despite the circumstances?