The Spirit and flesh are not friends, neither are they indifferent to each other. They are mortal enemies. We cannot mortify our sinful nature by doing good and thinking about positive things. The way in which the Bible teaches us to do this is right before us in this passage. It is by walking by the Spirit that we destroy the desires of the flesh. Romans 8:13 says, "by the Spirit [we] put to death the deeds of the body". Without The Work Of The Holy Spirit, there is no victory in our spiritual life.
That sanctification is progressive is seen in the fact that it is represented as a present reality and aim. So, the apostle Paul says that he is still pressing to make perfection his own (Phil. 3:12). It is something that he has not yet attained. In 2 Corinthians 3:18, Paul speaks about a most essential aspect of our growth in holiness: beholding the beauty of Christ. He speaks of us "beholding the glory of the Lord" and we "are being transformed into the same image from one degree of glory to another." This is a present reality. It is only in heaven or when the Lord comes back that we will perfectly be conformed to His image. John says that "we know that when he appears we shall be like him" (1John 3:2). Notice also how Paul begins in 2 Corinthians 3:18, "And we all, with unveiled face, beholding the glory of the Lord..." This is not a privilege for a few, but it is for all believers. He includes himself within the group which is beholding and being transformed. We may even say that he is being transformed even as he is beholding. He is being changed as he is enjoyed the infinite beauty of our Lord Jesus Christ.
In Ephesians 4, Paul uses the metaphor of a body reaching unity and maturity. God gave ministries to the church "to equip the saints for the work of ministry, for building up the body of Christ" (Eph. 4:12). Building up is not a short process, but in this case, a life-long process. This building up of the saints continues "until we all attain to the unity of the faith...to mature manhood, to the measure of the stature of the fullness of Christ" (Eph. 4:13). As long as we have sin our lives, we will need sanctification. The Scriptures teach that no one is sinless in this life (e.g. 1John 1:8-9). This shows us also that sanctification is incomplete in this life. Colossians 3 was also discussed above (see here), in which it is said that "the new self...is being renewed in knowledge after the image of its creator" (Col. 3:10). It is true that we were renewed in regeneration, but there is still a continual renewal through our life. The image will be the same only when we see Him (1John 3:2).
We may see that sanctification is progressive in another way, namely, in the commands of the New Testament to live holy. For example, Peter says:
1Pet 1:14-16 As obedient children, do not be conformed to the passions of your former ignorance, 15 but as he who called you is holy, you also be holy in all your conduct, 16 since it is written, “You shall be holy, for I am holy.”
Peter knows that those to whom he is writing are holy. He began his epistle by identifying them as "elect exiles", who were chosen "in the sanctification of the Spirit" (1Pet. 1:1-2). We are a holy priesthood and a holy nation (1Pet. 2:5, 9). Yet this does not mean that we are in no need of sanctification. There is both a ...