One can only offer their opinion and own interpretation, as this Epistle is a tricky one, as are St. Paul's others, as attested to even by St. Peter himself!
2 Peter 3:16
As also in all [Paul's v. 15] epistles, speaking in them of these things; in
which are certain things hard to be understood, which the unlearned
and unstable twist, as they do also the other scriptures, to their own
destruction.
St. Paul uses the word "law" three different ways in Romans 7:22-23 alone! (God's rules in general, perhaps the Law of Moses; what my fallen nature or concupiscence entices me to do; what my inner man or spirit wants me to do, but is held captive by this concupiscence)
So here is how I read St. Paul's argument (using Romans 7):
1 Know you not, brethren, (for I speak to them that know the law,)
that the law hath dominion over a man, as long as it liveth? 2 For the
woman that hath an husband, whilst her husband liveth is bound to the
law. But if her husband be dead, she is loosed from the law of her
husband. 3 Therefore, whilst her husband liveth, she shall be called
an adulteress, if she be with another man: but if her husband be dead,
she is delivered from the law of her husband; so that she is not an
adulteress, if she be with another man.
For I speak to them that know the law. That is, to Roman citizens who are well acquainted with laws in general, and living under them, as a highly regulated society. That the law hath dominion over a man, as long as it liveth. That is, where there is law, there is a subjugation by the law to live according to its rules. Where there is none, by implication, one is neither bound to any law, nor guilty of any crime (whether they ought to be held guilty is a separate question—moral law). For the woman that hath an husband, whilst her husband liveth is bound to the law. That is, by the bond or 'law' of a marital union. (St. Paul is stretching the term law deliberately to anything which regulates how we act or conduct ourselves or judge, in order to make his arguments relatable). But if her husband be dead, she is loosed from the law of her husband. If there is no law (the Greek word for law being in the masculine gender, making this first example fitting), there is no crime: but if her husband be dead, she is delivered from the law of her husband; so that she is not an adulteress, if she be with another man.
4 Therefore, my brethren, you also are become dead to the law, by the
body of Christ; that you may belong to another, who is risen again
from the dead, that we may bring forth fruit to God. 5 For when we
were in the flesh, the passions of sins, which were by the law, did
work in our members, to bring forth fruit unto death. 6 But now we are
loosed from the law of death, wherein we were detained; so that we
should serve in newness of spirit, and not in the oldness of the
letter.
You also are become dead to the law, by the body of Christ. The law has no power over someone no longer living in its domain. That you may belong to another, who is risen again from the dead, that we may bring forth fruit to God. That is, being "created in Christ Jesus unto good works." (Eph 2:10; John 15:5; 12:24) For when we were in the flesh. When we "[lived] according to the flesh." (Rom 8:13) The passions of sins, which were by the law, did work in our members, to bring forth fruit unto death. By the 'law of sin,' or the concupiscence proper to the human nature born in original sin—the percieved near-obligation to obey the sinful desires of the flesh or "earthly members" or 'earthly nature'. (Col 3:5) "When concupiscence hath conceived, it bringeth forth sin. But sin, when it is completed, begetteth death." (James 1:15)
But now we are loosed from the law of death, wherein we were detained; so that we should serve in newness of spirit, and not in the oldness of the letter. For to be born again in baptism is to "put off...the old man" (Eph 4:22). "For as many of you as have been baptized in Christ, have put on Christ." (Gal 3:27; John 3:5-6; 1 Pet 3:18-21). The law of death is a being doomed to a mere 'animal' life or nature, taken by original sin, not inspired and vivified by the life of grace which was lost after the Fall, which is now nonetheless offered and to be regained in New Testament redemption. The fallen human nature prone to sin (Rom 5:12).
In contrast to the oldness of the letter, which means adherence to 'the letter of the Law' as opposed to 'the spirit of the Law,' (2 Cor 3:6) which is grace administered by obedience thereto, now being offered via other means, namely the sacraments, which don't require works for recieving the grace administered therein; and the knowledge and relationship with the One who merited it for us, expounded upon and manifested in the New Covenant. (Eph 1:6-7) Which is the knowledge of what it is to follow God's laws for His sake, and not for sheer obedience to a legal system. (Mt 5:20-44). Serving God with a more mature and intimate knowledge of His desires and righteosness.
7 What shall we say, then? Is the law sin? God forbid. But I do not
know sin, but by the law; for I had not known concupiscence, if the
law did not say: Thou shalt not covet. 8 But sin taking occasion by
the commandment, wrought in me all manner of concupiscence. For
without the law sin was dead. 9 And I lived some time without the law.
But when the commandment came, sin revived, 10 And I died. And the
commandment that was ordained to life, the same was found to be unto
death to me. 11 For sin, taking occasion by the commandment, seduced
me, and by it killed me. 12 Wherefore the law indeed is holy, and the
commandment holy, and just, and good.
What shall we say, then? Is the law sin? God forbid. A law is not insufficient or broken because no one can keep it easily. It may rather imply the brokenness of those who can't keep it. This could refer to the Law of Moses, or even simply 'law' or 'legitimate or good laws.' But I do not know sin, but by the law; for I had not known concupiscence, if the law did not say: Thou shalt not covet. I don't feel the guilt, or I don't feel the compulsion to obey, or I don't feel I am trespassing any known law that has been sufficiently been made known to me: as any good law ought to be. If there was no law saying explicitly Thou shalt not covet, I might not have been so guilty for coveting; or I might not have been so tortured by conscience for having done it as often as I have.
But sin taking occasion by the commandment, wrought in me all manner of concupiscence. For without the law sin was dead. Taking occasion by the knowledge (having the law) that something truly is sinful, it makes what may otherwise have been a venial offense (not having full knowledge of the thing's sinfulness) a mortal sin. (1 John 5:16-17).
And I lived some time without the law. But when the commandment came, sin revived, and I died. For sin, taking occasion by the commandment, seduced
me, and by it killed me. When the commandments were made known to me, or when I was forced to be reminded of it, and I was aware of what was sin explicitly, the reality of sin revived, and I died spiritually; by its effects on my life, and under the weight of the guilt. And the commandment that was ordained to life, the same was found to be unto death to me. The commandment created for us to live by, and for us to obtain life by obedience thereto, became, as it were, my death, since I was forced to realize more and more that I had been doing was sinful and worthy of punishment. It is overwhelming to be aware that so many things are sinful to one degree or another. Wherefore the law indeed is holy, and the commandment holy, and just, and good. It is holy and right, and was given by none other than God. It was for our correction and life. And is good therefore. Good that it rightly convicts me of sin, which I deserve according to God's perfect justice.
13 Was that then which is good, made death unto me? God forbid. But
sin, that it may appear sin, by that which is good, wrought death in
me; that sin, by the commandment, might become sinful above measure.
Was that then which is good, made death unto me? God forbid. No, to call something good and just and holy, like the law of God, is to call good evil (Isa 5:20). But sin, that it may appear sin, by that which is good, wrought death in me; that sin, by the commandment, might become sinful above measure. That I may have the knowledge I ought to have according to justice, that that which is not right and offends God is sin, the law was put forth. That by the commadment I know what is sin, and that sin is real, and that I have sinned exceedingly. Which I ought to know, because I can therefore seek a way not to offend God further, and so severely, or often.
14 For we know that the law is spiritual; but I am carnal, sold under
sin. 15 For that which I work, I understand not. For I do not that
good which I will; but the evil which I hate, that I do.
For we know that the law is spiritual. The law is to do with morality and that which God expects of me as someone created in "His image," (Gen 1:27) to be moral like He is. (Eccl 7:29; Wis 2:23-24). But I am carnal, sold under sin. Captive to sin, I am a fallen man, with concupiscence. For that which I work, I understand not. "For the corruptible body is a load upon the soul, and the earthly habitation presseth down the mind that museth upon many things. And hardly do we guess aright at things that are upon earth: and with labour do we find the things that are before us. But the things that are in heaven, who shall search out?" (Wis 9:15-16) Thus, we need new spiritual strength, to restore the spirit's control over the body, which ought to be the servant of the spirit. For I do not that good which I will; but the evil which I hate, that I do. I can't do what I ought, and I do what I ought not and will not with my inner man, because of this 'law of sin in my members' or concupiscence. "This concupiscence, which the apostle sometimes calls sin...the...Church has never understood to be called sin, as being truly and properly sin in those born again, but because it is of sin, and inclines to sin."1
16 If then I do that which I will not, I consent to the law, that it
is good. 17 Now then it is no more I that do it, but sin that dwelleth
in me. 18 For I know that there dwelleth not in me, that is to say, in
my flesh, that which is good. For to will, is present with me; but to
accomplish that which is good, I find not. 19 For the good which I
will, I do not; but the evil which I will not, that I do.
If then I do that which I will not, I consent to the law, that it is good. By going against my conscience, I concede that the law justly convicts me, and is just. To pretend I don't know it's wrong now is foolishness. Now then it is no more I that do it, but sin that dwelleth in me. Not that I'm not the one guilty of sin, but if I will to obey my conscience with my inner man, it is my fallen nature and flesh that has a real part in me sinning. For I know that there dwelleth not in me, that is to say, in my flesh, that which is good. For to will, is present with me; but to accomplish that which is good, I find not. For the good which I will, I do not; but the evil which I will not, that I do. The flesh lets down and drags my spirit into that which I will not. (Mt 26:41).
20 Now if I do that which I will not, it is no more I that do it, but
sin that dwelleth in me. 21 I find then a law, that when I have a will
to do good, evil is present with me.
I find then a law, that when I have a will to do good, evil is present with me. And this is concupiscence. Like this, I am never able to please God and not sin!
22 For I am delighted with the law of God, according to the inward
man: 23 But I see another law in my members, fighting against the law
of my mind, and captivating me in the law of sin, that is in my
members.
For I am delighted with the law of God, according to the inward man. I take pleasure in knowing the just decrees and laws of God, because they are objectively good. And thus, were I unhindered by any contrary desire, I would keep them. But I see another law in my members, fighting against the law of my mind, and captivating me in the law of sin, that is in my members. My members—my fallen flesh, my corporeal component. It influences my desires, ever tempting me that keeping any law is difficult or contrary to me and what 'I' want. This hinders me from doing that which I want to do because it is just, and makes me want what I don't utlimately want!
24 Unhappy man that I am, who shall deliver me from the body of this
death? 25 The grace of God, by Jesus Christ our Lord. Therefore, I
myself, with the mind serve the law of God; but with the flesh, the
law of sin.
Unhappy man that I am, who shall deliver me from the body of this death? This is tragic: I'm a broken man, and am unable to keep the just law of God, which I ought. I need a radical solution—a nature-changing solution! What is it? The grace of God, by Jesus Christ our Lord. Therefore we have learnt that there is an inner desire to do the right thing (in those who dispose themselves to always at least seeking the right thing) but there is a disease which is the concupiscence and weakness of the fallen fleshly nature: Therefore, I myself, with the mind serve the law of God; but with the flesh, the law of sin.
These need to be ultimately harmonized. This is the Christian life. To bring the body into subjection to the spirit by chastizing it and brining it to heel. (1 Cor 9:27). Empowered by the grace of God. Restoring the original order, whereby a man is a spirit who has flesh, and not flesh which has a spirit, which it controls.
1 Council of Trent, Decree On Original Sin, 5.