Martin Luther said the gospel cannot be grasped well enough.
So, no matter how much gospel knowledge and affection you have, admit today that you have not arrived. You do not have a firm enough grasp on the gospel (and neither do I).
So, study the gospel, friends, study the gospel. Develop and enlarge your knowledge of and affection for the fact that Christ died for our sins.
One of the ways you can seek to strengthen your grip on the gospel is to read Bible-saturated books that seek to explain the gospel.
Here are some basic recommendations to get you started:
Beginners who are just beginning:
1. Living the Cross-Centered Life by CJ Mahaney
2. A Gospel Primer for Christians by Milton Vincent
3. Outrageous Mercy by William Farley
4. The Gospel for Real Life by Jerry Bridges
5. Fifity Reasons Why Jesus Came to Die by John Piper
Beginners who have already begun:
1. The Cross of Christ by John Stott
2. Redemption Accomplished and Applied by John Murray
3. God is the Gospel by John Piper
4. The Great Exchange by Jerry Bridges
5. In My Place Condemned He Stood by Packer and Dever
(This final book will then serve to point you to hundreds of other resources on the Gospel.)