Definition:
Internal transformation refers to the profound change that occurs within an individual as a result of spiritual renewal and the work of the Holy Spirit. This transformation is characterized by a shift in one's heart, mind, and spirit, aligning them more closely with the will and character of God as revealed in Scripture.

Biblical Basis:
The concept of internal transformation is deeply rooted in the teachings of the New Testament. It is often associated with the process of sanctification, where believers are progressively made holy through the work of the Holy Spirit.

1. Regeneration and New Birth:
The process of internal transformation begins with regeneration, often described as being "born again." In John 3:3, Jesus tells Nicodemus, "Truly, truly, I tell you, no one can see the kingdom of God unless he is born again." This new birth is a spiritual rebirth, marking the beginning of a transformed life.

2. Renewal of the Mind:
Romans 12:2 emphasizes the importance of mental renewal in the transformation process: "Do not be conformed to this world, but be transformed by the renewing of your mind. Then you will be able to discern what is the good, pleasing, and perfect will of God." This renewal involves a shift in thinking, aligning one's thoughts with God's truth.

3. Indwelling of the Holy Spirit:
The Holy Spirit plays a crucial role in internal transformation. In 2 Corinthians 3:18, Paul writes, "And we, who with unveiled faces all reflect the glory of the Lord, are being transformed into His image with intensifying glory, which comes from the Lord, who is the Spirit." The Spirit works within believers to mold them into the likeness of Christ.

4. Fruit of the Spirit:
Evidence of internal transformation is seen in the fruit of the Spirit, as outlined in Galatians 5:22-23: "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control." These attributes reflect the character of Christ and are cultivated in the believer's life through the Spirit's work.

5. Putting Off the Old Self:
Ephesians 4:22-24 instructs believers to "put off your former way of life, your old self, which is being corrupted by its deceitful desires; to be renewed in the spirit of your minds; and to put on the new self, created to be like God in true righteousness and holiness." This passage highlights the active role believers play in cooperating with the Spirit to shed sinful habits and embrace a new, godly way of living.

Theological Implications:
Internal transformation is not merely a moral or ethical change but a profound spiritual metamorphosis. It signifies a shift from living according to the flesh to living by the Spirit (Romans 8:5-6). This transformation is both instantaneous, at the moment of salvation, and ongoing, as believers grow in their faith and likeness to Christ.

Practical Application:
Believers are encouraged to actively participate in their transformation by engaging in spiritual disciplines such as prayer, Bible study, and fellowship with other believers. These practices help to cultivate an environment where the Holy Spirit can work effectively in their lives, leading to greater spiritual maturity and Christlikeness.

Conclusion:
Internal transformation is a central theme in the Christian life, reflecting the power of the Gospel to change hearts and lives. Through the work of the Holy Spirit, believers are continually being renewed and conformed to the image of Christ, demonstrating the transformative power of God's grace.