He's lying for Jehovah to the enemy:
http://wol.jw.org/en/wol/d/r1/lp-e/2013809?q=rahab+good+news&p=par
Her ruse worked! The king’s men hurried off in the direction of the fords of the Jordan. (Joshua 2:7) Rahab must have breathed a quiet sigh of relief. Using simple strategy, she had misdirected murderous men who had no right to the truth and she had saved innocent servants of Jehovah.
Rahab hurried back to her roof and told the two spies what she had done. She also revealed a vital fact: Her people had lost heart and were terrified of the invaders. This piece of good news must have thrilled the spies. Those wicked Canaanites were becoming terrified of the power of Israel’s God, Jehovah! Rahab then revealed something of even greater importance to us. She said: “Jehovah your God is God in the heavens above and on the earth beneath.” (Joshua 2:11) The reports she had heard about Jehovah were enough to teach her at least this much: Israel’s God was worthy of her trust. She put her faith in Jehovah.
To Rahab, there was no question that Jehovah would give his people the victory. So she begged for mercy, pleading that she and her family be spared. The spies agreed, stipulating that Rahab must keep their secret and must hang a scarlet cord from her window in the city wall so that the soldiers could protect her and her family.—Joshua 2:12-14, 18.
We can learn an essential truth about faith from Rahab. As the Bible puts it, “faith follows the thing heard.” (Romans 10:17) She heard reliable reports about the power and the justice of Jehovah God, so she put her faith and trust in him. Today, we have far more knowledge about Jehovah available to us. Will we seek to get to know him and put faith in him based on what we learn in his Word, the Bible?