Can someone who was previously saved and then walked away come back? Some verses in the New Testament seem to suggest this, such as the story of Peter denying Jesus three times but then repenting. How should we understand passages like Gal 2:17-18, and Heb 6:4-6?
This question involves at least two very large subjects, salvation and restoration. I can only touch on a few points and recommend some further reading. After outlining these subjects, I will comment briefly on the verses given in the second part of the question.
When speaking of those who have been saved, we need to realize that some who claim, or are said, to believe are not truly saved. In Matthew 13:1-9, we see that the Word had varying effects. Those who truly received the Word bore fruit. Also, in John 2:23-25, there were those who later proved that they were not true disciples. The most striking example is Judas who right from the beginning the Lord identified as “a devil”(Jn 6:70). In contrast, the Lord is emphatic regarding those who are true disciples that none could “take them out of his hand” nor “His Father’s hand.” (Jn 10:28, 29) So, the security of ones who have put their faith in the Lord Jesus Christ as their Savior is absolute. The fact that such a one is said to be “born again” and has “eternal life” is really the basis of that security (Jn 1:12, 13; 3:6-8; 3:16; etc.).
A true disciple may fail, even very badly, as shown in the history of the apostle Peter. Three instances come immediately to mind. In Matthew 16:23 the Lord had to reprimand Peter very sternly for allowing Satan to influence his thinking. Then, the Lord warned Peter that he would deny Him three times and so Peter did. (Jn 13:36-38; 18:15-18, 25-27.) Finally, in Galatians 2:11-14, we read that Paul had to reprimand Peter for his publicly hypocritical conduct. Yet, Peter was unquestionably devoted to the Lord. Many have walked contrary to the Lord for many years before coming to their senses and being restored to the service of the Lord.
There are a number of verses that are referred to when questioning the security of the believer. To keep this post to a reasonable length, I will look only at those given in the question.
In Galatians 2:17,18 close attention to the context is essential. The Galatians were attempting to bring law-keeping in as necessary for sanctification. Paul chided them strongly for trying to be made “perfect” by efforts of the flesh after they had “begun in the Spirit.” (Gal 3:1-4) This was in fact “another gospel” (Gal 1:6) than the one which he proclaimed to them (Gal 1:8). Notice that the context is Peter’s inconsistent behavior. The issue is not eternal salvation but sanctification. Remember that the apostle spent a good deal of his epistle to the Romans (ch 6-8) laying out the doctrine that our deliverance is completely dependent on God’s grace. That the apostle needs to remind us again in Galatians shows how hard it is for us to break free from the impulse of law-keeping as a basis for our acceptance with God, either for salvation or practical sanctification. This is a solemn lesson for us all.
Context is also very important for understanding the verses in Hebrews chapter 6. There are three critical observations. First, the epistle to the Hebrews was written to Jews who had joined the Christian company. There was a great danger that they had been impressed with the claims of Jesus as the nation’s Messiah and had joined for that reason without truly recognizing their personal need of Christ as Savior. Second, none of the conditions in verses 4 and 5 necessarily show a person to be a true disciple. Third, the verses following the ones cited in the question clarify the conditions under which verses 4 and 5 should be applied.
Five conditions are given in verses 4 and 5. A person may be “enlightened” in the sense of having understood in some measure the value of the gospel without receiving it for oneself. A person may have “tasted the heavenly gift” without having “eaten” (Jn 6:58). The “tasting” is a superficial reception. A person may have “shared in the Holy Spirit” by receiving external blessings from Him. A person may have “tasted the goodness of the word of God” by hearing its wondrous promises without realizing his own responsibility in them. A person may have shared in “the powers of the age to come” perhaps even by having been healed of some disease. All of these are external.
If we now look further down in the chapter we see there are two kinds of soil reminding us of the message of the Lord in Matthew 13. There the Lord warns that not all soil receives the seed of the Word. In some cases, there may even be an appearance of reception as the plant spouts but does not survive the heat of the day.
Finally, it is very important to notice that the writer concludes with “Though we speak in this way, yet in your case, beloved, we feel sure of better things—things that belong to salvation. For God is not so unjust as to overlook your work and the love that you showed for his sake in serving the saints, as you still do.” (vv 9, 10) The passage is not intended to unsettle the true disciple, rather it is a solemn warning for those who would join the Christian company carelessly and without regard for their personal relationship to the Lord.
Cutting, George, Safety, Certainty, and Enjoyment. Sunbury: Believers Bookshelf, (bbusa.org).
Wolston, W. T. P., God’s Restoring Grace. Sunbury: Believers Bookshelf, (bbusa.org).