Those who truly believe
By those who are in Christ Jesus, Saint Paul plainly means those who truly believe in him. He means those who, being justified by faith, have peace with God through our Lord Jesus Christ. Those who believe in this way no longer walk after the flesh. They no longer follow the motions of corrupt nature, but after the Spirit. Both their thoughts, words, and works are under the direction of the blessed Spirit of God.
1771 text
There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
1. BY them which are in Christ Jesus, St. Paul evidently means, those who truly believe in him: those who being justified by faith, have peace with God, through our Lord Jesus Christ. They who thus believe do no longer walk after the flesh, no longer follow the motions of corrupt nature: but after the Spirit: both their thoughts, words and works, are under the direction of the blessed Spirit of God.