You did not address this passage in Jethro's post:
Well; because of unbelief they were broken off, and you stand by faith. Be not high minded, but fear: For if God spared not the natural branches, take heed lest he also spare not thee. Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness,if you continue in His goodness: otherwise you also shall be cut off. And they also, if they abide not still in unbelief, shall be grafted in: for God is able to graft them in again. Romans 11:20-23
Paul is saying believers that have eternal life will be cut off the tree. As Yeshua said, a branch destined for the fire.
And you shall be hated of all men for my name's sake: but he that shall endure unto the end, the same shall be saved. Mark 13:13
Salvation is received by faith, but will become a reality after enduring until the end. Renouncing Yeshua is to no longer endure/abide and costs the faithless salvation.
Stand fast therefore in the liberty wherewith Messiah has made us free, and be not entangled again with the yoke of bondage. Behold, I Paul say unto you, that if you be circumcised, Messiah shall profit you nothing. For I testify again to every man that is circumcised, that he is a debtor to do the whole law. Messiah is become of no effect unto you, whosoever of you are justified by the law; you are fallen from grace. Galatians 5:1-4
Paul is addressing believers that have eternal life. If they choose to get circumcised in order to be justified by the law rather than by Messiah, Messiah's sacrificial blood atonement will be made void. It will not save them because they put their faith in their works rather than in Messiah.
For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Yeshua Messiah, they are again entangled therein, and overcome, the latter end is worse with them than the beginning. For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them. But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire. 2 Peter 2:20-22
Again, this refers to true believers who knew Yeshua and were in him. They turned away from Yeshua and his ways and returned back into the world. It would have been better for them to have remained unbelievers meaning, they are worse than unbelievers.