And do not be conformed to this world, but be transformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect. (Romans 12:2)
If you are a Christian, you are completely righteous before God. That is because your sins have all been forgiven, you have been justified and you have received the righteousness of Christ. Theologians call this "imputed" righteousness. It is a righteousness that cannot be earned, but is received by faith; But to the one who does not work, but believes in Him who justifies the ungodly, his faith is credited as righteousness. (Romans 4:5)
Following "justification" comes "sanctification", the growing and maturing process that brings our Christian practice into conformity with our righteous position. Ultimately, we are to be "glorified". This is all the work of the Holy Spirit that indwells the Christian; And these whom He predestined, He also called; and these whom He called, He also justified; and these whom He justified, He also glorified. (Romans 8:30)
We participate in our sanctification by resisting the temptations to be conformed to this world's sinful philosophy, culture and mores; in whose case the god of this world has blinded the minds of the unbelieving... (2 Corinthians 4:4). Rather than being conformed to this world, Christians are to submit to the transforming work of the Holy Spirit by fully trusting and obeying God's word.
How are you transformed? By the renewing of your mind. And how is your mind renewed? As we read and mediate upon the word of God, the Holy Spirit uses God's word to transform and sanctify us, renewing our minds so that we are no longer being conformed to this world, but are being transformed in our thinking, speaking and actions to that which is good and acceptable and perfect.
Sanctify them in the truth; Your word is truth.(John 17:17) Maranatha!