How can I increase in spiritual maturity?

TL;DR:

We can desire spiritual growth, but God alone has the power to actually change our hearts. God will transform us throughout our lives to be more spiritually mature; our part is to pursue and partner with Him as He matures us.

what does the bible say?

Spiritual maturity is a life-long process (Romans 7; Philippians 1:6), and God alone can transform us into more spiritually mature believers. We can, however, invite God’s change into our lives by working out our salvation (Philippians 2:12-13), practicing spiritual disciplines, and doing what Peter outlines in 2 Peter 1:5-7. Ultimately, we don’t have the power to spiritually mature on our own. The Holy Spirit holds this power (1 Thessalonians 5:12-22; 2 Peter 1:3),and He desires to transform us into Christlikeness as we abide in Christ.

from the old testament

In the Psalms, the theme of increasing spiritual maturity is evident through the psalmists' expressions of trust (Psalm 23:1-4), dependence on God (Psalm 25:4-5), and the deepening understanding of His character (Psalm 73:23-26).

from the new testament

We are burdened with our sinful flesh as long as we live on this earth, so our spiritual maturity will be a never-ending process. Paul expressed this dichotomy in Romans 7. At the same time, we have the assurance that God will develop spiritual maturity in us.
Paul makes it clear that the Holy Spirit's process of changing our hearts as we become more spiritually mature will take a lifetime (Philippians 1:6). We should humbly and joyfully receive the Holy Spirit’s work within us—even when that is painful.
God enables the journey to spiritual maturity. We have some responsibility, but He is the one who makes us like Jesus. Philippians 2:12-13 expresses both of these truths: "Therefore, my beloved, as you have always obeyed, so now, not only as in my presence but much more in my absence, work out your own salvation with fear and trembling, for it is God who works in you, both to will and to work for his good pleasure." Working out our salvation may involve practicing spiritual disciplines and cultivating our relationship with God.
In 1 Thessalonians 5:23-24, Paul writes under the inspiration of the Holy Spirit, "Now may the God of peace himself sanctify you completely, and may your whole spirit and soul and body be kept blameless at the coming of our Lord Jesus Christ. He who calls you is faithful; he will surely do it." While the previous verses (1 Thessalonians 5:12-22) admonish believers about spiritual maturity, Paul assures us that it is God who "will surely do it."
At the moment of salvation, we are fully equipped with everything needed for spiritual maturity. Second Peter 1:3 confirms this when Peter says, "His divine power has granted to us all things that pertain to life and godliness." He goes on to argue that "through [the promises of God] [we] may become partakers of the divine nature" (2 Peter 1:4).
In 2 Peter 1:5-7, we are told to "supplement your faith with virtue, and virtue with knowledge, and knowledge with self-control, and self-control with steadfastness, and steadfastness with godliness, and godliness with brotherly affection, and brotherly affection with love.” Then, verse 10 gives the result of this: "for if you practice these qualities you will never fall." God will change us to be more spiritually mature; our part is to pursue His change in us.

implications for today

Increasing in spiritual maturity means becoming more like Jesus, which is possible only when we become children of God and have the Holy Spirit living inside of us. The journey to spiritual maturity begins at salvation and will continue until we see Jesus face to face (1 John 3:2). God will take us on the journey to spiritual maturity as we commit to and abide in Him. A way of doing that is practicing spiritual disciplines, such as praying, doing Christian service, studying God’s word, and fellowshipping with other believers. These practices don’t save us, but they help us draw closer to God. The Holy Spirit alone gives us the desire to be more like Christ and does the work of transformation in us.

understand

Spiritual maturity is a lifelong process, initiated and sustained by God.
The Holy Spirit transforms us toward Christlikeness.
We grow spiritually mature by pursuing God and partnering with Him in what He is doing in our lives.

reflect

What does it look like to actively partner with God in your journey toward spiritual maturity?
In what areas of your life do you feel God is calling you to grow spiritually?
How can you cultivate a deeper dependence on God, trusting Him to transform you into Christlikeness?

engage

What spiritual disciplines help us grow in spiritual maturity, and how can we encourage one another in practicing them consistently?
How does the Holy Spirit's work in our lives shape our understanding of spiritual maturity as a community of believers?
How does our personal spiritual maturity impact those around us?