You tell a child who is misbehaving (or even an adult, sometimes), “O grow up!” Paul, in Ephesians 4:14–16, summons you to Christian maturity.
Grow up! Don’t stay a toddler. Infancy is normal—for a time. Don’t forget that at the beginning of our Christian walk we all were infants. And being a baby Christian is far different from being an unbeliever. However, don’t be satisfied with spiritual immaturity. Christ has blessed his church with word-gifts so that you can grow in maturity. Paul thinks of the weakness and lack of coordination of an infant: “Support her head!” He will expand on the maturation process shortly. The immaturity is also compared to a small boat driven about and influenced, in this case not by the waves of a storm, but by the winds of false teaching. The cults are superb at concealing what they want to. Paul uses strong language to condemn those who are apparently self-consciously leading people astray.
Instead, live truthfully in love. Paul has in view not just physical maturity and coordination, but the development of character as well. Instead of being easily led and influenced, a maturing young person begins to look beyond the self-centeredness of infancy. Although “speaking the truth in love” may express the idea, don’t limit what Paul says to speech. He will expand on speaking in love, see verse 25. Here action is included as well as speech. “Living in truth and love,” or “truthing in love” might express the idea. In any case, what Paul is describing involves a concern for union with Christ and for relationships with other believers. These need to be characterized by love. Don’t use Paul’s command as an excuse to avoid confronting falsehood—look at the context of verse 14. But also be careful in how you differ with those you believe may be in error. God is no less concerned with how we oppose error than he is with the fact that we do oppose it. John, in his first epistle, speaks of love as defining, not just Christian maturity, but Christianity itself. Paul comes back to the term in verse 16.
Grow in Christ. Grow into Christ. How do you measure growth? Not by marks on a door frame, but by a person. While growth involves each of us as individuals, it is also something corporate. We together grow into the Head, that is Christ. The doctrine of the church is important. The church, though it has an invisible aspect (all who are truly in Christ), also is a visible body, where real people are interacting and serving one another. It a place were we encourage one another and help hold one another accountable. That means that membership in the church is important. If the image of the church as a strengthening body works, it is because central to the body is the head. Christian maturity involves a clearer, more self-conscious relationship with Christ. Union with Christ defines you. This growth in Christ affects all areas of your life. It happens “in all things.” Nothing that you are or do is not related to him.
“Christ did not ascend to heaven in order to enjoy a quiet vacation at the right hand of God, for, like the Father, he always works (John 5:17). He went to heaven to prepare a place for his own there and to fill them here on earth with the fullness that he acquired by his perfect obedience. What he received as a reward for his labor for himself and what he received for his own cannot be separated. He is all and in all (Col. 3:11). The pleroma (fullness) that dwells in Christ must also dwell in the church. It is being filled with all the fullness of God (Eph. 3:19; Col. 2:2, 10). It is God whose fullness fills Christ (Col. 1:19), and it is Christ whose fullness in turn fills the church (Eph. 1:23). The church can therefore be describe as his pleroma, that which he perfects and gradually, from within himself, fills with himself (Eph. 4:10), and is therefore itself being filled by degrees. As the church does not exist apart from Christ, so Christ does not exist without the church.”
Herman Bavinck, Reformed Dogmatics, Vol. 2, page 474
Not only do you grow into Christ, you grow from Christ. Paul uses enough athletic imagery that you know that he appreciates what the body can do. Instead of early, wobbling steps, picture a young man running his heart out, or making a move on a basketball court. Picture a young woman performing a triple Lutz on the ice rink, or blocking a rifle shot of a volleyball. All of this activity is connected to the head. True, the athlete doesn’t stop to think, but the eye catches the flight of the line drive, the brain calculates location and timing, then orders the body into motion, leaping and stretching horizontally to make the catch—all faster than one can describe. The head is crucial to the process of growth, and coordinates how the body functions. Paul keeps pushing you back to the basics—Christ working through the Word that he has given his church. Christ working by his Spirit in enabling the preaching and teaching of that Word as the basic means of grace.
Do grow up, so that together the church can function in ways that truly glorify her Lord.