Are all followers of Christ guaranteed sanctification (1 Thess. 5:23-24 vs. 2 Peter 2:20-22)?
Answer: Sanctification is contingent upon our sustained faith (1 Jn. 1:7, 9).
That is, 1) No we are not guaranteed sanctification if we fall away (the point of 2 Pet. 2:20+), and 2) yes, we can most definitely lose our salvation if we choose to abandon it (Col. 1:23, etc.).
Suppose we read the two sets of passages together:
2 Peter 2:21-22: "For it would be better for [the apostate Christian] not to have known the way of righteousness, than having known it, to turn away from the holy commandment handed on to them. It has happened to them according to the true proverb, 'A DOG RETURNS TO ITS OWN VOMIT,' and, 'A sow, after washing, returns to wallowing in the mire.'”
1 Thessalonians 5:23-24: "Now may the God of peace Himself sanctify you entirely; and may your spirit and soul and body be preserved complete, without blame at the coming of our Lord Jesus Christ. Faithful is He who calls you, and He also will bring it to pass."
I suggested elsewhere, that the following response may be unpalatable to some. Now (as before), it is never my intent to wound those who believe we can simply never be lost once we receive salvation in Christ. However, the far greater imperative is for the truth to prevail -- something that surpasses the sensitivities of those who may disbelieve it.
It makes no difference if we add another set of passages (1 Thess. 5) to cloud the issue. This merely introduces another level of complexity. It is to the apparent misunderstanding of passages like these two which I speak. It is certainly true that, as long as we "walk in the Light" (1 Jn. 1), we are sanctified (set apart as holy) while "[our] spirit and soul and body ]is] preserved [without] blame [at Christ's return]" (1 Thess. 5:23).
Note that this pronouncement is nearly identical to Paul's words in the Letter to the Colossians:
Colossians 1:22-23: "[Christ] has now reconciled you in His fleshly body through death, in order to present you before Him holy and blameless and beyond reproach— if indeed you continue in the faith firmly established and steadfast, and not moved away from the hope of the gospel.
Here, he makes the point more emphatically. However, note the conditions upon which this holiness rests: "[If] indeed you continue in the faith firmly established and steadfast, and not moved away from the hope of the gospel." This directive could not be much clearer.
Here, allow me to point out several instances where we are told that someone can, indeed, fall away from the faith. And, in doing so, they are in a perilous condition because, no, they are no longer sanctified (set apart and purified as holy).
1. In the John's Gospel, Jesus proclaimed:
John 15:2, 6: “Every branch in Me that does not bear fruit, He takes away; and every branch that bears fruit, He prunes it so that it may bear more fruit."
6“If anyone does not abide in Me, he is thrown away as a branch and dries up; and they gather them, and cast them into the fire and they are burned" (emphasis added).
Is Christ not warning his disciples that anyone who does not abide in Him -- that is, in all His commandments, will be "gathered and cast into the fire where they are burned"? Is that fire not Hell? How else can we possibly read this? Is someone who accepted Christ and was baptized only to later decide to lead the life of an unrepentant criminal still saved, still sanctified? Has this person not, as with 2 Peter 2:20-22, metaphorically returned to "his own vomit" to "wallow in the mire"?
2. In Paul's Letter to the Galatians, the apostle warned that if these Christians continued to abandon their faith in favor of the Law of Moses, the Gospel would be useless:
Galatians 5:2: "Behold I, Paul, say to you that if you receive circumcision, Christ will be of no benefit to you" (emphasis added).
If Christ is "of no benefit" to Christians who looked back to the Old Law, how then can they be spared from eternal separation with God? This is followed by another stern warning from Paul:
Galatians 5:4: "You have been severed from Christ, you who are seeking to be justified by law; you have fallen from grace" (emphasis added).
Is not "being severed from grace" essentially the same thing as "being no longer sanctified"? Is it possible to ignore the words "severed from Christ" and "fallen from grace"? And, if we are severed or have fallen from Christ, does this not mean we are lost in eternal flames? Is there some "safety net" that will still catch the ex-Christian as they plunge headlong into Hell? If these admonitions are unconvincing, just what will ever convince someone that yes, we can fall away from the faith, no longer sanctified?
3. Perhaps the "go to" Book of the Bible in the matter of apostasy is the Letter to the Hebrews. There, we read several grave warnings:
Hebrews 2:1-3: For this reason we [Christians] must pay much closer attention to what we have heard, so that we do not drift away from it. For if the word spoken through angels proved unalterable, and every transgression and disobedience received a just penalty [in the O/T], how will we escape if we neglect so great a salvation [in Christ]?"
This passage is asking, if we "drift away" from the faith which we now possess, how will we escape the wrath of God? If I decide to denounce -- for life -- my Christianity, have I not "drifted away" from (indeed, jettisoned) my faith and sanctification? If not, how so? Are we to actually believe that God will refuse my denunciation?
4. Again, in the Letter to the Hebrews, we are cautioned never to develop faithlessness:
Hebrews 3:12: "Take care, brethren [Christians], that there not be in any one of you an evil, unbelieving heart that falls away from the living God" (emphasis added).
From this verse, the clear implication is that we can develop an evil, unbelieving heart that **falls away from God." And, if we do this, we will never enter into paradise with Him. It seems to me that to believe otherwise may constitute a certain spiritual blindness.
5. Later, in chapter 6 of the same Letter we read:
Hebrews 6:4-6: "For in the case of those who have once been enlightened and have tasted of the heavenly gift and have been made partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, and then have fallen away, it is impossible to renew them again to repentance, since they again crucify to themselves the Son of God and put Him to open shame" (emphasis added).
If the clause of verse 6 above ("then have fallen away") does not mean what it says, how then do words have meaning? Clearly, this passage is speaking of those who received the Gospel and were then sanctified. They "were made partakers of the heavenly gift [of Christ]," and have "fallen away" from Him. The writer then warns that it is impossible for someone in this state to be renewed as long as they persist in their present, fallen condition. Obviously, then:
Hebrews 6:8: "[If this person] yields thorns and thistles [produces worthless fruit to God], [they are] worthless and close to being cursed, and end up being burned."
How is someone in such a condition saved? Can we really employ textual gymnastics to somehow modify the meaning of the text? Or is it not the case that when someone turns to a life of willful disobedience, they are "putting the Son of God to open shame" (6:6)? As chapter 10 of the same Letter explains:
Hebrews 10:26-27: "For if we go on sinning willfully after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, but a terrifying expectation of judgment and THE FURY OF A FIRE WHICH WILL CONSUME THE ADVERSARIES" (cf. Isa. 26:11, 1 Thess. 1:7, emphasis added).
There should be no doubt that if someone falls away from their faith in Christ, there is no longer any sacrifice for their sins unless they return to Him. All that is left is "a terrifying expectation of judgment."
6. Too often, we rely on the advice of those who seem to casually dismiss biblical texts of the clearest importance. Everyone should understand the meaning of 2 Peter 2 in the OP:
2 Peter 2:20-22: "For if, after they have escaped the defilements of the world by the knowledge of [Christ], they are again entangled in them and are overcome, the last state has become worse for them than the first… It has happened to them [apostates] according to the true proverb, “A DOG RETURNS TO ITS OWN VOMIT,” and, “A sow, after washing, returns to wallowing in the mire” (emphasis added).
Those who fall away from the faith are in a much more severe state than they were before they received Christ in the first place. I suggest the text of 2 Peter 2 could not be clearer in this regard.
These passages only scratch the surface of the truth that saints can fall away; 1 Thessalonians 5 adds nothing to alter the fact, as indeed is stated even more emphatically in Colossians 1:23. We should ask ourselves -- not based on someone else's opinion, -- not what we have been told, but rather on our own eyes: How do these passages (and many more) not speak directly to those who have received the gift of grace from God as stated in the verses of 1 Thessalonians 5:23-24, and have then forsaken it? Is such a person, unrepentant in their denunciation of God, really saved whatsoever? If so, how?
It is truly a wonder that anyone is unable to discern this "forest for the trees."