I've picked up and started working through (again) Steven Smallman's The Walk. I hope to use this book to help others along the way, but I was freshly reminded of the importance of the gospel for the disciple to continue to grow in Christ. He writes, "Do you want to become Jesus' disciple? Repent, believe the gospel, and follow Jesus. Do you want to grow stronger as a disciple of Jesus? Repent, believe the gospel, and follow Jesus."
The gospel is every bit as applicable for the believer as for the unbeliever!