The following comes from a public facebook note by Dr. Robet A. J. Gagnon:
How the Reformed Doctrine of the Perseverance of the Saints Approach Undermines NT Warnings about Potential Loss of Salvation
Those who promote the Reformed doctrine of the perseverance of the saints (much less a doctrine of once-saved-always-saved that doesn't require a transformed life) as an ironclad guarantee that true believers can never fall away, have two basic options: Either (1) they don't apply the warnings to believers, at least not as warnings about not inheriting God's kingdom; or (2) they vitiate such warnings in a way that Jesus and NT authors never did, by immediately assuring their audience that, no, a genuine believer can't actually fall away.
These warnings appear all over the NT witness (multiple times in nearly every NT book, minus some one-chapter books), threatening with loss of eternal life or the Kingdom of God even those professed believers acknowledged to have at one time received the Spirit of Christ. Obviously they undermine the view of the inevitable perseverance of the saints, so it is natural that they would fall into disuse in Reformed circles.
The best Reformed scholars and pastors within the second camp don't try to dismiss the warnings as applying only to those who appear to be believers (but are not) or as referring only to loss of extra rewards in heaven. They acknowledge that most of the warnings both (1) apply to genuine believers, not just those who profess to be believers but are not; and (2) refer to loss of eternal life or inheritance in the Kingdom of God, not just to getting a few less goodies in heaven.
When they apply these warnings to believers (whether just professed or apparently genuine), they add that these warnings are used by God, through their urgency and severity, to keep true believers from falling away, without exception.
The thinking is: If believers think that they could fall away by not living a transformed life in the Spirit, then they will get a sense of the urgency and severity of a situation of ongoing sin and will make the appropriate changes to stay in the fold, and thus accomplish God's purpose in having the saints persevere.
But then comes the problem: These Reformed scholars and pastors, when citing these warnings, immediately give reassurance that true believers can never really fall away.
What is the problem with this? By reassuring believers that, if they made a genuine conversion, they can't really fall away, Reformed scholars and pastors "let the cat out of the bag," so to speak (assuming for the sake of the argument their position of POTS to be correct). That is, while warning believers living immoral lives that they risk not inheriting God's kingdom, they at the same time offer reassurance that true believers can't lose a salvation that they genuinely received at the time of conversion. In doing so, they vitiate the intended effect of the warnings in their original context.
These warnings have their salutary effect only by making believers think that they really could fall away if they don't continue to follow the leading of the Spirit. The situation is urgent, with eternal ramifications. Yet the need for moral reform and repentance becomes much less urgent, and the potential consequences far less severe, when one then adds, "Don't worry: God will absolutely prevent you from falling away if you are a real believer, and I have seen significant signs and evidence of that in your life."
I believe that Jesus, Paul, and the NT writers generally do give assurances of confidence that those believers to whom they are speaking will indeed endure to the end. But these assurances are not carte blanche, ironclad guarantees. And that's the difference from what happens in the Reformed camp.
God does indeed provide believers with all the power and inspiration necessary for persevering to the end. But the situation is not irrevocable. Once-genuine believers can fall away, because they are not programmed robots but independent agents with free will.
If they do fall away, it is through no fault of God's or Christ's. If they remain, it is entirely due to the provision of grace, power, love, patience, and deliverance made available to God. To God alone is the glory. And yet believers must still cooperate with the meritorious work of God to save them. And not all do.
If you don't like the fact that I and others don't subscribe to an ironclad guarantee of the perseverance of the saints that effectively eliminates the necessity of their cooperating will, think of it this way: All we are doing is what Jesus and the apostles were doing when they tried to convince believers with warnings that they could indeed fall away if they didn't continue to walk in the Spirit rather than in the sin-infiltrated flesh. Don't shoot the messenger.