I've just finished preaching through the book of Exodus and wanted to share some of my experience preparing for and then preaching from it. Exodus for many people is a foreign country. After Creation and then the stuff about Abraham and his kids, it becomes a bit of a blur of rules, weird stories and bloody sacrifices. Although interestingly, unlike Leviticus, sacrifice is not a big theme in Exodus. If you had to summarise the book into one phrase it would be 'being rescued into God's presence' and forms a magnificent sequel to Genesis. If you're a preacher it also roughly divides into two separate and manageable series', the rescue from Egypt chapters 1-16, and then instructions for living in God's presence chapters 17-40.
One of the advantages of preaching from the Old Testament is you can use its exotic unfamiliarity to create rhetorical tension. The only time this doesn't work is when the material seems both alien and irrelevant. So, for example, everyone is keen to hear how you'll handle the 10 commandments but less interested in the relevance of priestly garments and tabernacle construction. The juicier passages that feature strict regulations, violence or weird rituals can be preached very simply, by presenting the strange potency of the material and then resolving the tension on a case by case basis. (More on that below.) The priestly garments and tabernacle instructions are trickier because you need to highlight our sinful condition first and then show why these things are necessary before finally linking them to their fulfilment in Jesus.
People over-complicate the Old Testament. But here are two tricks that help with preparation and then presenting the rhetoric of the gospel as you understand and apply the Old Testament. Firstly treat the Old Testament like the New Testament or Watership Down or Lord of the Rings or any other great text. Admittedly, the stakes are higher with Scripture, God, the cosmos and life and death.You might read The Prince by Niccolò Machiavelli carefully but hopefully, you won't let it change your life! Essentially, you consider the audience, it's meaning and the authorial intent. In other words, what is the text saying to the '1st hearers', us the '2nd hearers', what's the underlying principle and what is the purpose of the passage? You do exactly the same with the New Testament. The second trick is to beware of continuity and discontinuity between the old and new covenants. Some things continue, some things are different. Sometimes it'll be obvious (e.g High Priest), at other times you'll have to hold both in tension (e.g 2nd Commandant). Jesus has completely fulfilled the Law, but it's still a good thing, showing us God's holiness and our own sinfulness, among other things.