And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness (Romans 8:10).
Anyone who has the Spirit not only is called Christ’s, but even has Christ Himself.
For it cannot but be that where the Spirit is, there Christ is also.
For wheresoever one Person of the Trinity is, there the whole Trinity is present.
For It is undivided in Itself, and has a most entire Oneness.
What then, it may be said, will happen, if Christ be in us?
The body is dead because of sin; but the Spirit is life because of righteousness.
You see the great evils that come of not having the Holy Spirit; death, enmity against God, inability to satisfy His laws, not being Christ’s as we should be, the want of His indwelling.
Consider now also what great blessings come of having the Spirit: being Christ’s, having Christ himself, vying with the angels (for this is what mortifying the flesh is), and living an immortal life, holding henceforward the earnests of the Resurrection, running with ease the race of virtue.
For he does not say so little as that the body is henceforward inactive for sin, but that it is even dead, so magnifying the ease of the race. For such a one without troubles and labours gains the crown.
Then afterward for this reason he adds also, “[dead] to sin”, that you may see that it is the viciousness, not the essence of the body, that He has abolished at once.
For if the latter had been done, many things even of a kind to be beneficial to the soul would have been abolished also. This however is not what he says, but while it is yet alive and abiding, he contends, it is dead.
For this is the sign of our having the Son, of the Spirit being in us, that our bodies should be in no respect different from those that lie on the bier with respect to the working of sin.
But be not affrighted at hearing of mortifying. For in it you have what is really life, with no death to succeed it: and such is that of the Spirit.
It yields not to death any more, but wears out death and consumes it, and that which it receives, it keeps it immortal.
And this is why after saying the body is dead, he does not say, but the Spirit “lives”, but, “is life”, to point out that He (the Spirit) had the power of giving this to others also.
Then again to brace up his hearer, he tells him the cause of the Life, and the proof of it. Now this is righteousness; for where there is no sin, death is not to be seen either; but where death is not to be seen, life is indissoluble.
John Chrysostom (c.347-407): Homilies on St Paul’s Epistle to the Romans, 13 (on Romans 8:10); [slightly adapted].