I asked my good brother, Jon, what he thought of the term “mature Christian” and what he thinks makes a mature Christian or not. He wrote me a pretty awesome response and I thought I’d share because who knows… Maybe this will be a blessing to someone.
"Hiyo. Ha, that’s a very interesting question, because the term does get misunderstood a lot in the ways it is thrown around.
First, I think it has to be established that while there are more mature and less mature Christians, everybody is equally infinitely distant from the perfect standard who is Jesus Christ (“For all have sinned and fallen short…” Romans 3:23). So no matter where you are in your walk with Jesus, we are all “more sinful than you could ever dare imagine and you are more loved and accepted than you could ever dare hope-at the same time.” – Tim Keller. This keeps us humble without being self-deprecating. In ourselves, we have much sin, yet our identity is not in our sin, but our savior. And because of Jesus’ death, God loves us as though we have always obeyed perfectly because we have been given Jesus’ righteousness (2 Corinthians 5:21/Philippians 3:9).
Second, any growth in maturity is by the sheer grace of God, so that nobody can boast either in their initial salvation or their sanctification (“By the grace of God I am what I am…” 1 Corinthians 15:10).
Third, because it’s all grace, more mature Christians can’t boast or look down on those who are less mature. Spiritual disciplines like reading God’s Word, prayer, fasting, and simple obedience don’t earn, merit, or achieve greater spiritual position before God. We don’t try to become more like Jesus so God likes us more or sees us as better than other Christians – we want to become more Christ-like because we love Him and desire to honor His name and glorify Jesus Christ.
Fourth, the marks of maturity aren’t just external signs of grace (breadth of theological knowledge, ministry skillset, life experience, abundance of Christian activities like prayer meetings, evangelism, etc.) but first internal signs of grace, which I’d say is character: Christ-likeness, shown by the fruit of the Holy Spirit (love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control; Galatians 5:22). This emphasis can be seen in Jesus’ teaching where the first commandment is to love God and others (Matthew 22:37), and when he was about to be crucified, the last thing he did was humble himself to wash the disciples feet (John 13) and tell them to love one another (John 13:34).
In my own experience, these emphases are often lacking, so it can result in measuring maturity in quantitative terms (how much you’re doing, how many people are professing Christ, etc.) without first focusing on quality: how well Christians know the love of their Father and how well they love Him and others in return.
Quantity is important, but having a bunch of Christians that have very little fruit of the Spirit isn’t really fulfilling the Great Commission (“teaching them ALL I have commanded you” Matthew 28:20). Plus, Jesus said that our love is a means by which more people come to know of Jesus: “By this all people will know that you are my disciples, if you have love for one another” (John 13: 35)