One cannot be "in Christ" and continue in the flesh. Yes, we are not God, we are still in human form, in that sense we are still "flesh", yet not all flesh is = sin or sinfulness. God's qualm is not in how He made us, but in our rebellion to Him and our bent to sinning.
"And the Word became flesh and dwelt among us, and we beheld His glory, glory as of the only begotten from the Father, full of grace and truth." Jn. 1:14.
Knowledge of being in Christ has a purpose other than forgiveness. Regeneration, conversion, repentance, the New Birth speak of a real change in the individual to a purpose; holiness, God-likeness, character change.
"No one who abides in Him sins; no one who sins has seen Him or knows Him. Little children, let no man deceive you; the one who practices righteousness is righteous, just as He is righteous; the one who practices sin is of the devil;..." 1 Jn. 3:6-7.
God demands holiness in the believer, so when God
"saves to the uttermost" he fails because your flesh is too powerful for Him? Being saved to the uttermost is much more than some cosmic transaction, it is a real change in the believer from darkness to light, from sin to holiness.
Flesh is no longer king when a believer is saved. God is enthroned, the Holy Spirit abides and directs the believer.
Scripture speaks of several things concerning a believer. First, it speaks of coming to Christ to have our sins forgiven. But the Bible does not stop there! It constantly and consistently seeks to align the Believer with God's nature; holiness.
As He is, so are we in this world. (1 Jn. 4:17). Yes, one has to be forgiven, be converted, repent, receive a new nature through regeneration; the New-Birth. This is salvation, but the central idea of Christianity is not regeneration; it is holiness. It is the highest state in which Scripture claims a believer can (through grace and the work of God in their lives) become! Why command obedience, why demand holiness, why all the pleading to remain in Christ if there is nothing left to do for the regenerate, Born-Again Believer?
If this is not true, then the vast majority of the Bible from Romans through Revelation has no real meaning.
Unbeliever's are told to repent, believe, have faith, and get saved. Believers are exhorted to remain in the faith, abide in Christ, lay hold on eternal life, continue in Christ, be holy, be perfect in love, sin not, we are to: "Follow peace with all men, and holiness, without which no man shall see the LORD: Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled;" Hebrews 12:14-15.