Historically, the book of Exodus treats of the deliverance of Israel from Egypt; but viewed doctrinally, it deals with redemption. Just as the first book of the Bible teaches that God elects unto salvation, so the second instructs us how God saves, namely, by redemption. Redemption, then, is the dominant subject of Exodus. Following this, we are shown what we are redeemed for-worship, and this characterizes Leviticus, where we learn of the holy requirements of God and the gracious provisions He has made to meet these. In Numbers we have the walk and warfare of the wilderness, where we have a typical representation of our experiences as we pass through this scene of sin and trial-our repeated and excuseless failures, and God's long-sufferance and faithfulness.
