One of the more important truths I've been learning over the past several years is that the Gospel isn't just for unbelievers. It's something that I, as a believer, need to be reminded of every day.
Here's how Bryan Chapell puts it in Christ-Centered Worship: Letting the Gospel Shape Our Practice:
While the gospel includes the good news of God's grace for those who would turn to him in faith, the gospel is not just for outsiders or unbelievers. Great power lies in the line popular among young Christians today: "We must preach the gospel to our hearts every day." This ethic is not just about repeating those portions of the gospel that lead to new conversions; it is about engaging the power of the good news that God has provided his grace to save, to sanctify, and to equip his people for this day, every day, and forever. We need this gospel to enter Christ's kingdom, but we also need it to walk with him through our daily trials and demands.