To preach the gospel to yourself means that you continually face up to your own sinfulness and then flee to Jesus through faith in His shed blood and righteous life.
It means that you appropriate, again by faith, the fact that Jesus fully satisfied the Law of God. In both its precepts and penalty, He fulfilled the Law of God in its most exacting requirements. And He did this in our place as our representative and our substitute. He is your propitiation, so that God’s holy wrath is no longer directed toward you.
To preach the gospel to yourself means that you take at face value the precious words of Romans 4:7-8: “Blessed are those whose lawless deeds are forgiven, and whose sins are covered; blessed is the man against whom the Lord will not count his sin.”
You believe on the testimony of God: “There is therefore now no condemnation for those who are in Christ Jesus” (Romans 8:1).
You believe that “Christ redeemed us from the curse of the law by becoming a curse for us” (Galatians 3:13). You believe He forgave you all your sins (Colossians 2:13), that He reconciled you “to present you holy and blameless and above reproach before him” (Colossians 1:22).
To preach the gospel to yourself means you appropriate by faith the words of Isaiah 53:6: “The LORD has laid on him the iniquity of us all.”
It means you dwell upon the promise that God has removed your transgressions from you as far as the east is from the west (Psalm 103:12), that He has blotted out your transgressions and remembers your sin no more (Isaiah 43:25).
Gerald and Jerry Bridges. Holiness Day by Day: Transformational Thoughts for Your Spiritual Journey Devotional (p. 40). Kindle Edition.