Assurance is a tricky thing in the Christian life. There are numerous ways we can gain assurance. With regards to assurance, there are two things I try to prevent: a false believer from thinking he is a real one and a real believer from thinking he is a false one. This is not easy, as false believers are not easily convinced of their true state and true believers often have great doubts. However, I think preaching in such a way that Christ's work and his commands are presented is the best way to guard against either error. Below I present two different types of preaching and what I think are the effects these types of preaching will have. I will admit it is simplistic and there are other things that could and should be added. But I think the main point will be clear. These thoughts were prompted as I preached through Ephesians 4:25-5:2.
Here are the two preaching scenarios: In the first, there is a preacher who believes that he must preach Christ. His sermons focus around Jesus and his work on the cross. They focus on what he did to save us and redeem us. This preacher looks for Jesus in every text, including the Old Testament ones. The primary application to every one of his sermons is "Trust in Christ or keep trusting in Christ." He does not normally exhort men to be obedient. He thinks this will lead them to trust in themselves instead of Christ. He does not preach against gossip or lying. He does not say that the sexual immoral will burn in the lake of fire. (Revelation 21:8) He sticks to what Jesus has done.He believes that if he does this men will turn from their sin as they trust in Christ.
The second man also wants to preach Christ. But he believes preaching Christ does not mean preaching only what Jesus has done upon the cross, but also how we should live because of what Jesus has done. He does not believe calling his flock to live obediently will necessarily lead to legalism. So he preaches the crucifixion and resurrection as the only hope of mankind. But also preaches against gossip, lying, sexual immorality, pride, wrath, laziness and a host of other sins. He reminds his people that Christ has conquered those sins and that because they trust in him they are to be a new kind of people who are killing sin in their lives by the power of the Spirit.