Rahab.

Rahab the prostitute. The story of the fall of Jericho is one of my favorite stories. But it would have been impossible without the faith of a prostitute. Rahab hides two Israeli spies from the guards of the city and is saved from death and destruction by her faith. But, the really crazy part of the story is that Rahab is included in the lineage of Christ. Joshua 2:14-21 describes the incident:
¹⁴ “Our lives for your lives!” the men assured her. “If you don’t tell what we are doing, we will treat you kindly and faithfully when the LORD gives us the land.”

 ¹⁵ So she let them down by a rope through the window, for the house she lived in was part of the city wall. ¹⁶ She said to them, “Go to the hills so the pursuers will not find you. Hide yourselves there three days until they return, and then go on your way.”

 ¹⁷ Now the men had said to her, “This oath you made us swear will not be binding on us ¹⁸ unless, when we enter the land, you have tied this scarlet cord in the window through which you let us down, and unless you have brought your father and mother, your brothers and all your family into your house. ¹⁹ If any of them go outside your house into the street, their blood will be on their own heads; we will not be responsible. As for those who are in the house with you, their blood will be on our head if a hand is laid on them. ²⁰ But if you tell what we are doing, we will be released from the oath you made us swear.”

 ²¹ “Agreed,” she replied. “Let it be as you say.”

   So she sent them away, and they departed. And she tied the scarlet cord in the window.

Rahab is spoken of as a person of faith in Hebrews 11:31 and good works in James 2:25. In Matthew 1:5 she is named as the mother of Boaz and included in Christ's lineage.
The Old Testament is full of examples of God using the faithfulness of even the most fallen and corrupted people. His love, forgiveness, and covenant is tied throughout the history of the world. AND HE WILL NEVER BREAK IT! No matter if we are prostitutes, liars, thieves, etc. Christ's reign is sovereign and pure and our sins are nailed to the cross. That's the truth of Christmas.