To preach the gospel to yourself means that you take at face value the precious words of Romans 4:7-8:
Blessed are they whose transgressions are forgiven, whose sins are covered. Blessed is the man whose sin the Lord will never count against him. (Bridges, 59 -- see previous posting)"When you set yourself to seriously pursue holiness, you will begin to realize what an awful sinner you are. And if you are not firmly rooted in the gospel and have not learned to preach it to yourself every day, you will soon become discouraged and will slack off in your pursuit of holiness."