The following is taken from a public post on facebook from Robert A. J. Gagnon:
I was asked by a FB friend: "What response would you give to the view that says the warnings are for a loss of rewards in the Kingdom, not a falling away?"
My answer:
That is a question that cannot be answered in general, but must be answered by a careful exegesis of each individual warning. So my answer can be found for each posting involving exegetical analysis. I will give three examples from Paul, the apostle of grace.
A. 1 Cor 9:24-27:
"Do you not know that those who are running in a stadium are all running but (only) one receives the prize? Be running like this in order that you may convincingly receive it. Now everyone who competes exercises self-control in every way. So those people (do it) in order that they may receive a perishable wreath but we an imperishable one. Hence I am running like this: … I whip my body into shape and bring it into subjection (as though my slave), lest somehow, after proclaiming to others, I myself should come to be disqualified." (GET)
(1) "The prize" is called "an imperishable wreath" and is distinguished from an earthly "perishable wreath." The prize is thus imperishability, or eternal life, in the Kingdom of God. The only other use of the adjective "imperishable" (aphthartos) in 1 Corinthians describes the acquisition of imperishability that comes with the resurrection from the dead (15:52-55). And the only uses of the abstract noun "imperishability" (aphtharsia) also refer to the resurrection from the dead (1 Cor 15:42, 50, 53-54; cp. Rom 2:7; 2 Tim 1:10). Paul then in 1 Cor 9:24-27 is not distinguishing between different levels of imperishable existence but between not receiving imperishability (resurrection) and receiving it.
(2) Similarly, in Phil 3:8-14, "the prize" (brabeion, used only in 1 Cor 9:24 and Phil 3:14 in the Bible) is spelled out again as the resurrection from the dead. Paul also speaks similarly here of a rigorous regiment needed in order to attain this prize, which prize he stresses he has not yet attained and even might not attain should he lapse in this regiment.
(3) That the prize in 1 Cor 9:24-27 is imperishable life is evident also from his application of this point to his warnings aimed at the Corinthians. The Corinthians apparently hold something akin to the modern OSAS view. Paul recounted to them the Old Testament story of the destruction of the wilderness generation as God’s judgment for their involvement in idolatry and sexual immorality (1 Cor 10:1-13).
The point of Paul’s midrash (exposition) of Israel’s disastrous desert wanderings after their exodus from Egypt is clearly to warn the Corinthians not to become presumptuous through some eternal security doctrine. Israel’s wilderness generation had tokens of salvation comparable to that of the Corinthian believers: a “baptism” of sorts “into Moses” as well as partaking of “spiritual food and drink.” Yet because of engaging in idolatry and sexual immorality hardly any of them made it to the promised land—an image that prefigures not inheriting the kingdom of God in the age to come.
Paul’s point is to warn the Corinthians: Even though you have been incorporated into Christ and regularly confirm that relationship in the celebration of the Eucharist, you too could still fall if you persist in idolatry (compare the rebuke in the rest of ch. 10 about not going to an idol’s temple) and sexual immorality (compare the case of the incestuous man in chs. 5-6).
Paul does not encourage the Corinthians to reassure themselves that they could never fall away. On the contrary he insists that “the one who thinks that he stands should watch out lest he falls.” The prospect of falling is real. It is the reason for the all-too-genuine warning. What is at stake for the Corinthian believers? Paul has already told them in 6:9-10: The sexually immoral and idolaters will not inherit the kingdom of God.
B. Galatians 5:2-4
"Look, I, Paul, am saying to you that if you get circumcised Christ will be of no help to you. And I call as a witness again to every man who gets circumcised that he is a debtor to do the whole law. You were discharged from (the employ/service of) Christ, you who are trying to be justified in (the domain/sphere of the) law. You fell out of grace."
Paul has already acknowledged that they "received the Spirit" at the time they embraced the gospel (3:1-5). He doesn't ask them whether they received the Spirit; he asks them how they received the Spirit, by doing the deeds stipulated by the Law of Moses to be done or by believing the gospel message.
And yet he asks the Galatians incredulously, "having begun with the Spirit, are you now ending with the flesh? Did you experience such things in vain?" Paul is using expressions applicable only to those whom he believes to be genuine believers, since only genuine believers can have the Spirit of Christ.
In 5:2-4 Paul states that the Galatian Christians whom he has already established have the Spirit of Christ will, if they now get circumcised and take on the yoke of the law of Moses:
--be "discharged from the employ of" Christ
--have "fallen out of grace"
--no longer have Christ be of "help" or "benefit" to them.
This language clearly presupposes once having been genuine Christians. One can't "fall out of" something that they were never in, nor be "discharged from Christ" when one was never employed by him to begin with.
When Paul goes on to warn these genuine believers again that those whose life is characterized by "the works (deeds) of the flesh," things "about which I am telling you beforehand, just as I told you beforehand, that those who do such things will not inherit the kingdom of God" (5:19-21), there can be no denying that he is aiming his remarks at believers whom he acknowledges have received the Spirit of Christ. He is once more warning these genuine believers who have the Spirit that if they become "sexually immoral" or "idolatrous" or engage in destroying the community of faith by their dissensions, they will not inherit eternal life.
When he in 6:7-9 tells the very same Christians whom he has admitted received the Spirit of Christ when they believed the gospel to "stop deceiving themselves," that God will not be "mocked" or "sneered at," that if they "sow into the field of their flesh they will reap a harvest of destruction" rather than "eternal life," it is obvious that he yet again is warning genuine believers not to lose eternal life.
C. Romans 11:17-24
In 11:17-24 Paul uses the metaphor of a cultivated olive tree whose roots are the patriarchs (Abraham, et al.) as a symbol of the sphere of salvation. "Some" Israel branches were "broken off" because of "unbelief" with respect to the Messiah Jesus. Gentiles who have come to faith in Christ have been grafted in, as though coming from a less impressive "wild olive tree." Their grafting in clearly illustrates the genuineness of their place "in Christ" through the gift of the Spirit and forgiveness of sins.
And yet Paul warns them not to "brag" with respect to the fate of "some" of the Israel branches. "For if God did not spare the natural branches, neither will he spare you" who were not a natural part of the cultivated olive tree. They will experience "the kindness of God if you remain on in that kindness; otherwise, you too will be cut off," that is, removed from the sphere of salvation that till now they have enjoyed.
Clearly that illustrates that even Gentile believers can be removed from the sphere of salvation in Christ if they don't continue in faith. Nothing is irrevocable. Indeed, Jews who were removed for unbelief with respect to the Messiah "can be grafted back in if they do not remain on in their unbelief."