The Apostle Paul
Romans 8:13BSB·traditional attribution

For if you live according to the flesh, you will die; but if by the Spirit you put to death the deeds of the body, you will live.

John Calvin Reformed @genevareformer

13. For if ye will live after the flesh, etc. He adds a threatening, in order more effectually to shake off their torpor; by which also they are fully confuted who boast of justification by faith without the Spirit of Christ, though they are more than sufficiently convicted by their own conscience; for there is no confidence in God, where there is no love of righteousness.

Matthew Henry Presbyterian @wholebiblehenry

In these verses the apostle represents two more excellent benefits, which belong to true believers. I. Life. The happiness is not barely a negative happiness, not to be condemned; but it is positive, it is an advancement to a life that will be the unspeakable happiness of the man (Rom 8:10, Rom 8:11): If Christ be in you. Observe, If the Spirit be in us, Christ is in us.

Commenting on Romans 8:10-16

John Gill Reformed Baptist @doctorgill

For if ye live after the flesh, ye shall die,.... Such persons are dead, whilst they live, and shall die a second or an eternal death, if grace prevent not. It may be asked, whether one that has received the grace of God in truth, can live after the flesh; flesh, or corrupt nature, though still in such a person, has not the dominion over...