He suggests that we preach the Old Testament believers not as moral exemplars, but as examples of those who lived by faith:
Preaching Christ from all the Scriptures joins faith to grace. The Old Testament believers trusted as they waited for that salvation to come. They are examples to us as believers – not apart from the objective facts of God's redemption, but as those who lived by faith.
The obedience of love flows from that faith relation. Like faith, love is kindled not by introspection, but by looking to Jesus, the Author and Finisher of our faith. We love because He first loved us; it is the love of God that is shed abroad in our hearts.
Preaching Christ also helps us avoid moralism and other fads:
The Scriptures are full of moral instruction and ethical exhortation, but the ground and motivation of all is found in the mercy of Jesus Christ. We are to preach all the riches of Scripture, but unless the center holds all the bits and pieces of our pulpit counseling, of our thundering at social sins, of our positive or negative thinking – all fly off into the Sunday morning air.
Paul was resolved to know nothing at Corinth but Jesus Christ and Him crucified. Let others develop the pulpit fads of the passing seasons. Specialize in preaching Jesus!