In Paul's writings the way of the believers' growth in life is revealed in much more detail than in Peter's writings. According to Paul's writings, the believers grow in life by drinking the spiritual milk (1 Cor. 3:2a; Heb. 5:12b), by eating the spiritual food (Heb. 5:14a), by drinking the Spirit (1 Cor. 12:13b), by being watered (1 Cor. 3:6b, 7b), and by God operating in them (Phil. 2:13). The believers also grow in life by Christ living in them and making His home in them (Gal. 2:20a; Eph. 3:17a). Christ is not only living in us but also making His home in us. He desires to get Himself settled within us.
The believers grow in life also by the Spirit of Jesus Christ supplying bountifully in them (Phil. 1:19b). With the Spirit of Jesus Christ there is a rich and bountiful supply in everything.
The believers grow in life also by the growth of God (Col. 2:19). As we grow in the divine life, God also grows in us. Since God is complete and perfect in Himself, we may wonder why God needs to grow. It is true that God is complete and perfect in Himself, but He is not complete and perfect in us. In most of us God is too little. How much God do you have within you? Only God knows the answer to this question. Nevertheless, we all need to allow God to grow in us.
Finally, in Paul's writings the believers grow in life by the supply out from the Head, Christ (Eph. 4:16a). We are members of the Body of Christ. While we as members are growing, Christ the Head is supplying. Out from the Head we receive the supply for us to grow in life. In our spiritual life, day by day we need to eat sufficiently, rightly, and properly to receive the supply from Christ the Head. We all need to practice eating, drinking, and breathing. We also need to learn how to rest. To be healthy we need five things: eating, drinking, breathing, resting, and exercising. If we do these five things in our Christian life, we will be spiritually healthy and will surely grow in life.