Have you heard sermons that use Old Testament stories as allegories to Christian life? How about Bible Study groups that do so? I remember attending a women's Bible Study group back in the early 1980s, in which we used Alan Redpath's book, Victorious Christian Living as a study guide for the book of Joshua. According to Redpath, the book of Joshua illustrates the progression from salvation (crossing the Red Sea with Moses) to sanctification (possessing the Promised Land).
For instance, Redpath compared Joshua's victory over the five Amorite kings in Joshua 10:16-27 to our triumph over various sins as Christians. As Joshua executed the king, so Christians must slay our sins (never mind that Jesus already put sin to death through His death on the cross, as Colossians 2:14 explains). By minimizing Joshua 10:16-27 into an allegory, Redpath soothed our post-Vietnam War sensibilities as he assigned us an unscriptural responsibility for our own sanctification.
The Old Testament certainly has lessons that the Lord expects Christians to apply, as Paul asserts in 1 Corinthians 10:6, but it is really an historical book, not a series of analogies. Through the various accounts, we see man's depravity, and we also see the Lord's patient determination to have a holy people. Joshua killed Canaan's inhabitants, not to symbolize a Christian response to sin, but because God didn't want them to lead Israel into idolatry.
Redpath, and teachers like him, encourage us to liken ourselves to Joshua. Scripture, on the other hand, simply presents Joshua as the historical leader who led Israel into the Land that God gave to Abraham. Reading the entire Old Testament has the value of revealing the Lord's character through His relationship with Israel (and Judah), but we shouldn't fabricate analogies out of every story. The New Testament writers tell us when Old Testament events serve as allegories, and we can leave it there as we appreciate the Lord's wonders in the narrative.