Falling from Grace is a warning passage from Paul In Galatians 5:6 You are severed from Christ, you who would be justified by the law; you have fallen away from grace.
It means you are cut off from Christ if you put yourself back under the law. But it doesn't mean you have to stay there, or even go there. That's why it's called a warning passage.
Gal 5:6 is just one of the many passages (I will list more below) that speak of losing our salvation. This one tells that if we seek to put ourselves back under the Old Covenant and subject to the Law of Moses then we are cut off from Christ and lose the salvation that we had when we were in Christ.
I agree that we do not have to stay there, but if we do (as some argue that we are on this site) then we are cut off from God's grace and have lost our salvation.
For many people “falling from grace” is synonymous with losing salvation. This perception is unfortunate and misleading. Equally unfortunate is that the majority of people I talk to about “falling from grace” have no idea where the phrase came from or to what it originally referred. In most cases they aren’t even sure where they first heard it. “Doesn’t the Bible say you can fall from grace?” Is what I usually hear.
I agree that people should not use terminology that they do not understand, and they should study the Word to know what it says. I have never been good at remembering book, chapter, and verse, but I do remember what Scripture says, so I can quickly look up the reference for the subject I am discussing. But you are correct that many people do not study the Word for themselves.
To compound the problem, these three words have become a common expression for losing favor with someone. All of this together has resulted in a great deal of confusion over this phrase, which appears only once in the New Testament and was never intended to be lifted from the text as a theological maxim. To understand this highly misunderstood expression, one must study out its one and only context.
The book of Galatians finds Paul defending himself and the gospel of Christ from a group of “teachers” who arrived in Galatia sometime after he left. The group, commonly referred to as the Judaizers, proclaimed a gospel different from Paul’s. Yet it was similar to the apostle’s teaching in enough ways to confuse the Christians in Galatia.
The group believed and taught that salvation was found through having faith in Christ along with keeping portions of the law. Their distorted gospel centered on the importance of circumcision. Paul’s letter indicates that the Judaizers were successful in persuading some gentile believers to be circumcised to ensure their salvation.
I know it's hard to believe but there are still Judaizers around today preaching a different gospel.
You are correct in your evaluation of who, what, and why Paul was addressing the congregation in Galatia. And if this were the only Scripture that speaks of losing salvation, then I could agree with you that we could not lose our salvation.
However, there are many other passages that point to losing the salvation that is in Christ.
Heb 6:4-6 - Clearly those
"who have once been enlightened and have tasted of the heavenly gift and have been made partakers of the Holy Spirit" are saved. And the point Paul makes is that if someone falls away they cannot be restored to repentance.
2 Pet 2:20 - Again,
"after they have escaped the defilements of the world by the knowledge of the Lord and Savior Jesus Christ" is clearly indicative of those who have been saved. Yet if they are entangled and overcome again in sin, then they are worse off than if they had never been saved in the first place.
2 Tim 2:11-12 - Paul tells Timothy,
"The statement is trustworthy: For if we died with Him, we will also live with Him; If we endure, we will also reign with Him; If we deny Him, He will also deny us." If we endure then we will reign. If we (the Church) deny Him, then He will deny us.
James 5:19-20 -
"My brothers and sisters, if anyone among you strays from the truth and someone turns him back, let him know that the one who has turned a sinner from the error of his way will save his soul from death and cover a multitude of sins." Anyone among you (the saved in the Church) who strays from the truth will be lost if he is not turned back to the Way by someone willing to speak truth into his life and bring him back. That person saves a soul (would have been lost).
Rom 11:22 -
"See then the kindness and severity of God: to those who fell, severity, but to you, God’s kindness, if you continue in His kindness; for otherwise you too will be cut off." Once someone has been grafted in (saved), he must continue in belief and obedience to God or he can and will be cut off from salvation again.
These are just a few, and there are many others, but these clearly show that salvation can be lost if we do not continue in Christ.