Although we have no record of any sermon that Noah preached, the apostle Peter tells us that Noah was a "preacher of righteousness" (2 Pet. 2:5). Whether or not Noah ever preached a sermon, there is another way in which it can be said that he was a herald, proclaimer, or preacher of righteousness.
Noah was an upright man in the midst of a wicked world (Gen. 6:5-9). By the very life that he lived, he "condemned the world" (Heb. 11:7). His uprightness of life was a stark and condemning contrast to the wickedness that existed around him. As we continue to live righteous lives in this wicked world, we are preaching righteousness.
Noah spent 120 years building an ark which would deliver himself and his family from destruction. No doubt this ark was often the source of ridicule that Noah received from his wicked neighbors. However, it stood as a monument to his righteousness, and, when judgment came, it was his source of deliverance. We are not building an ark, but day by day we are building a righteous life. Our faithful obedience to God will one day deliver us from judgment to come, but today it serves as a monument of righteousness in the world.
The life that we live sends a message. Does it preach righteousness in a world of darkness and sin? Do we, by our daily conduct, "prove what is that good and acceptable and perfect will of God" (Rom. 12:2)? Or do we blend in with this lost and dying world, extinguishing our light and rendering our salt tasteless and worthless (Matt. 5:13-16)?
"That you may become blameless and harmless, children of God without fault in the midst of a crooked and perverse generation, among whom you shine as lights in the world" (Phil. 2:15).