This is crucial, because it is not uncommon for Christians to find real discouragement and weariness as the years of life go on and they fight some of the same struggles with sin, doubt, fear, and temptation year after year. Many Christians have not been taught that the Gospel is the power that is meant to sustain them and refresh them day after day. They try to change themselves by force of will, or through guilting themselves and punishing themselves with shame when they make mistakes. God has a much better plan and solution for us than this. Milton Vincent gives a very illuminating but simple and accessible overview of this in his short book A Gospel Primer for Christians.
He wrote his book "as a correction to a costly mistake made by Christians who view the gospel as something that has fully served out its purpose the moment they believed in Jesus for salvation. Not knowing what to do with the gospel once they are saved, they lay it aside soon after conversion so they can move on to 'bigger and better' things (even Scriptural things). Of course, they don't think this is what they are doing at the time, yet after many years of floundering in defeat they can look back and see that this is exactly what they have done."
"On the most basic of levels, I desire fullness[.]"