"Christ is become of no effect unto you, whosoever of you that are justified by the law; ye are fallen from grace." Galatians 5:4
The majority of the religious world is made up of those who believe the lie that a person can lose their salvation. These people number in the BILLIONS who believe this. Most of them do not have the exact answer concerning how a person loses their salvation, but when pressed they have to agree it is by sin of some sort, to some extent. How many sins or what kind of sins is never specified. Some of them say sins that are not confessed or repented of after salvation will send the person to eternal condemnation.
The word of God defines sin as transgression of the law (I John 3:4). People who believe that sin (however many not specified) after salvation will cause a loss of salvation are really saying you must keep the law to be saved or at least to maintain salvation. The word of God says that whoever is under the law is under a curse (Galatians 3:10). The scriptures also plainly tell us that we cannot ever be saved by keeping the law (Galatians 2:16, 3:11 & Romans 3:20).
Any way of salvation that has its basis in us not sinning, in other words: keeping the law, as a condition is a false gospel and a condemning curse that falls short of grace. It is not a gospel of "good news" but rather the worse news you can hear. It is salvation that is conditioned on or based on the work or merit of the sinner. The scripture clearly teaches that salvation is NOT by works (Romans 4:5-6, 11:6, Galatians 5:4, Ephesians 2:8-9, Titus 3:5). So their message from the start does not even qualify as a gospel of grace that God will use to convert sinners to Himself but rather is a false message that can only stir up the wrath of God against them. NOBODY can be saved that believes in this false gospel or any other. That means those billions of religious people who think salvation can be lost, are lost, and in false religion needing to be evangelized.
The worse part about a message that says you can lose your salvation is it says the merits of the obedience and death of Christ were not enough to save a person eternally but that the sinner must supplement salvation. They are showing that their god cannot get it done so they have to help their poor god out by their obedience and law keeping. Almighty God allows NO boasting, bragging, or glory in the sinner at all in true salvation. Salvation is of the LORD from start to finish. His merit of blood and righteousness established and imputed will get the job done forever. All other ways of self-righteous works are ways of death and condemnation! Run fast away from salvation based on human works and trust in the victorious and complete work alone of the God-man, Christ now.