You just cannot cease to personally attack Sabbath keepers. I know of no Sabbath keeping believers posting here that have rejected Messiah Yeshua. You do Satan's work to accuse the brethren falsely.
Yes, the Sabbath is a "perpetual covenant" aside from the Old Covenant. It is also a sign given by our Creator that we may know it is He (YHWH) who sets us apart (sanctifies us) from the rest of the world (verse 13). Why would anyone in their right mind want to do away with such a blessed sign?
You err by not knowing Scripture and by taking this passage out of context. This passage is only the beginning of Paul's argument which continues throughout chapters 7 & 8. In Romans 7:21-23, Paul identifies the law he is referring to.
Rom 7:21 I find then a law, that, when I would do good, evil is present with me.
Rom 7:22 For I delight in the law of God after the inward man:
Rom 7:23 But I see another law in my members, warring against the law of my mind (the law of God/Torah), and bringing me into captivity to the law of sin which is in my members.
It is the law of sin that we must die to before we can marry Yeshua.
Rom 8:2 For the law of the Spirit of life in Messiah Yeshua hath made me free from the law of sin and death.
Once we are freed from that
other law, we can marry Yeshua. We then become spiritually minded people in contrast to those that are still carnally minded people that refuse to subject themselves to the law of God/Torah.
Rom 8:6 For to be carnally minded is death; but to be spiritually minded is life and peace.
Rom 8:7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be.
Rom 8:8 So then they that are in the flesh cannot please God.
You better hope there is grace for law breakers because you are the greatest law breaker of all since you profess to have no law, not even New Covenant law.
Again, you take Paul's words out of context. He is not saying we frustrate grace by obeying the law. He is saying we frustrate grace
by seeking to be justified/made righteous by our law keeping instead of being justified by faith. It is faith that causes the fruit of our salvation to come forth, that is, obedience to the law. That is why Paul said, "Do we then make void the law through faith? God forbid: yea, we establish the law." Romans 3:31