This is going to be a long one.
First and foremost, I am going to keep saying this until someone finally hears me!
When it talks about the adulterer, the liar, the sorcerer, the homosexual, not inheriting the Kingdom of God, it is talking about those who are NOT in Jesus Christ. Those who are NOT saved. Those who ARE saved are NO LONGER those things. We are righteous IN CHRIST. WE ARE SAVED IN CHRIST. We are made righteous by the power of Jesus Christ and by the power of Jesus Christ alone.
Observing the laws of Moses does nothing but make people stumble, because it was by that old covenant that sin was made aware, but even then the promise to Abraham came BEFORE THE LAW WAS EVEN KNOWN. Faith was at work before Moses, sin was at work before the law of the letter. Works were before the law! Works are living our faith! Faith comes by belief! Salvation comes by belief! Repentance comes from belief! It is not repent then come before the Cross is it!? Has it ever been?! I think not! It is and always has been come before the Cross and then repentance shall come! The work of salvation comes to us when we put our BELIEF in Christ. Not when we put our works of the law into action! Not when we choose to follow a Sabbath, not when we choose refrain from eating certain foods, works do not beget faith! Faith begets work! Works without faith is fruitless, and faith without works is dead, but those who have faith will find plenty of works at their hands!
NO ONE HAS THE POWER TO TAKE THOSE WHO ARE SAVED, MADE RIGHTEOUS IN CHRIST, OUT OF THAT SALVATION. NO SIN, NO ACTION BY MAN SHALL EVER OVERPOWER THE WORK OF THE CROSS. IT IS COMPLETE, IT IS ETERNAL, IT IS FOREVER.
We are saved through faith in Jesus Christ and his work on the cross, and I might quickly add, continuing in faith in Jesus Christ and his work on the cross, and nothing else.
Read Paul's parable of the olive tree in Romans. Also read Peter's writings, in which he clearly talks about people losing their salvation. "falling from their steadfastness", "dog returning to its vomit", "sow returning to wallow in the mire". Paul: "if God spared not the natural branches take heed lest he spare not thee also."
First, let's address Paul talking about the olive tree, since you seem to lump several verses together.
Romans 11:17-24 NIV
"17If some of the branches have been broken off, and you, though a wild olive shoot, have been grafted in among the others and now share in the nourishing sap from the olive root, 18do not boast over those branches. If you do, consider this: You do not support the root, but the root supports you. 19You will say then, "Branches were broken off so that I could be grafted in." 20Granted. But they were broken off because of unbelief, and you stand by faith. Do not be arrogant, but be afraid. 21For if God did not spare the natural branches, he will not spare you either.
22Consider therefore the kindness and sternness of God: sternness to those who fell, but kindness to you, provided that you continue in his kindness. Otherwise, you also will be cut off. 23And if they do not persist in unbelief, they will be grafted in, for God is able to graft them in again. 24After all, if you were cut out of an olive tree that is wild by nature, and contrary to nature were grafted into a cultivated olive tree, how much more readily will these, the natural branches, be grafted into their own olive tree!"
You say this is talking about salvation. That someone can lose it, yet however we see over in Hebrews...
Hebrews 9:23-28 NIV
"23It was necessary, then, for the copies of the heavenly things to be purified with these sacrifices, but the heavenly things themselves with better sacrifices than these. 24For Christ did not enter a man-made sanctuary that was only a copy of the true one; he entered heaven itself, now to appear for us in God's presence. 25Nor did he enter heaven to offer himself again and again, the way the high priest enters the Most Holy Place every year with blood that is not his own. 26Then Christ would have had to suffer many times since the creation of the world. But now he has appeared once for all at the end of the ages to do away with sin by the sacrifice of himself. 27Just as man is destined to die once, and after that to face judgment, 28so Christ was sacrificed once to take away the sins of many people; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him."
Ok, since Christ didn't die multiple times for multiple sins, but once for all sin, then all sins we've ever committed or ever would commit were paid for on the Cross. So with that in mind, it becomes clear that Paul IS NOT talking about salvation there! So what then is he talking about? He is talking about those who are in Christ who act in an unholy way will not be subject to God's grace or mercy in events resulting from their inequity. Though should that person return from their sin, God will accept them and they will enter His good graces again. That, however, does not mean their salvation has become moot, far from it.
Why is that? Becauuuuuuse...
Romans 8:1-4 NIV
"1Therefore, there is now no condemnation for those who are in Christ Jesus,[
a] 2because through Christ Jesus the law of the Spirit of life set me free from the law of sin and death. 3For what the law was powerless to do in that it was weakened by the sinful nature,[
b] God did by sending his own Son in the likeness of sinful man to be a sin offering.[
c] And so he condemned sin in sinful man,[
d] 4in order that the righteous requirements of the law might be fully met in us, who do not live according to the sinful nature but according to the Spirit."
Therefore stop telling people their salvation is at risk! God is a good Lord who will keep His own. They will be disciplined for their actions, for the Lord is also a Father to us now. Now, as for your bit about Peter talking about that...
2 Peter 2:1-
"1But there were also false prophets among the people, just as there will be false teachers among you. They will secretly introduce destructive heresies, even denying the sovereign Lord who bought thembringing swift destruction on themselves. 2Many will follow their shameful ways and will bring the way of truth into disrepute. 3In their greed these teachers will exploit you with stories they have made up. Their condemnation has long been hanging over them, and their destruction has not been sleeping."
Peter is NOT talking about Christians losing their salvation! He is talking CLEARLY about those who call themselves Christians who are in fact wolves in sheeps clothing, deceivers and liars, who will be punished for their trespasses!
People, I'm not trying to cause problems here, I'm wanting people to see the truth that is evident in scripture itself. All I'm doing here is retelling what I have read. You're right about the fact we shouldn't go on and do whatever we want as far as sin goes, but as far as things as what we call Holy days or what we eat, don't worry about that. That's between the person and God, it is a matter of faith. The written code is done away with, but the law of the Spirit is in effect. Sin is still sin. Those who betray their nature by giving into their temptations will fall, and fall hard. Only in Christ will they ever be able to stand again, and even then He will not abandon them. In their lowest moments they will remember Him. Even if they die from their actions, Christ will not abandon them for it. It then falls back to what Paul said. Their works will be caught up in fire, but they themselves shall survive. So let's stop spreading the ideas of legalism, or that Christians can be abandoned by God, because quite simply, it is unBiblical, and unChristian.
Peace and Love in Christ our Holy Lord.