Romans 8:5-8
[5] Those who live according to the sinful nature have their minds set on what that nature desires; but those who live in accordance with the Spirit have their minds set on what the Spirit desires. [6] The mind of sinful man is death, but the mind controlled by the Spirit is life and peace; [7] the sinful mind is hostile to God. It does not submit to God's law, nor can it do so. [8] Those controlled by the sinful nature cannot please God.

Sanctification is the change God makes in our lives as we grow in the faith. We have to understand the seriousness of sin. God’s forgiveness does not make sin less serious. We are either controlled by our sinful natures, or we will  follow after the Holy Spirit.
 

 1 Cor. 2:12-16
[12] We have not received the spirit of the world but the Spirit who is from God, that we may understand what God has freely given us. [13] This is what we speak, not in words taught us by human wisdom but in words taught by the Spirit, expressing spiritual truths in spiritual words. [14] The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned. [15] The spiritual man makes judgments about all things, but he himself is not subject to any man's judgment:
[16] "For who has known the mind of the Lord that he may instruct him?" But we have the mind of Christ.

No one can understand God, but through the Holy Spirit, we can have insight into what some of God's plans are for us. Are you spending enough time with Christ to have his very mind in you? Philip. 2:5 Let this mind be in you, which was also in Christ Jesus: