Rahab enters the redemptive story simply by hiding the spies and telling them when and where to go. The most profound part of this story is when she told the spies all about Yahweh and that when Israel came to take their land like Yahweh promised, they should spare her. They agreed making a binding covenant between Israel and Rahab.
I say that Rahab had more faith than the spies and even Joshua. If Joshua had faith, he wouldn't have sent the spies! But, Rahab knew what God would deliver through on his promise.
God used Rahab the Harlot to further the Upper and Lower Story! Rahab is important in our faith because she demonstrated enough faith, despite being of ill-repute, that God chose her to to be in the lineage of David and eventually Jesus.