Eph 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
Paul's is using an analogy of a "sealed document" back then. When you sealed a document, you sealed it with wax and it was sealed until it was delivered to the proper recipient. Paul was using an analogy of an inheritance in a legal will, which would have been properly witnessed and sealed by a representative of the Roman government.
When a document like this is received, the first thing that is observed is whether or not the seal is intact. If the seal was broken then the representative would know that some tampering occurred and the document would be considered void and the inheritance denied.
This is Paul's analogy. We must protect our covenant with God and not seek to break the seal of the Holy Spirit. A GREAT Official (Holy Spirit) seals the document but a common citizen can tamper with it and break the seal.
Was it possible for a Roman citizen to break the wax seal? Of course it was. This is also true of one who breaks the seal of the Holy Spirit. That is why blasphemy of the Holy Spirit is the only sin that cannot be forgiven. If you look at various verses that speak of falling away, you will see that this sin against the Holy Spirit is linked to Apostasy.
Heb 6:4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
Heb 6:5 And have tasted the good word of God, and the powers of the world to come,
Heb 6:6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
Heb 10:29 29 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?
This is why Paul warned us not to tamper with our seal.
30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
This is a big problem with Christendom, today. A false security is being preached. Once sealed, always sealed. The Word of God does not agree nor support that. Remember, these letters are written to Followers of Christ. The Early Church did not believe OSAS.
Here are some examples:
1 Tim 1:19-20
19 Holding faith, and a good conscience; which some having put away concerning faith have made shipwreck:
20 Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme.
Paul warned Timothy to guard his faith. He stated clearly that some had abandoned their faith and shipwrecked. Then he named two acquaintances, Hymenaeus and Alexander, who became apostates by blaspheming the Holy Spirit.
Did you know that the Word of God says that our faith can be overthrown?
2 Tim 2:16-18
16 But shun profane and vain babblings: for they will increase unto more ungodliness.
17 And their word will eat as doth a canker: of whom is Hymenaeus and Philetus;
18 Who concerning the truth have erred, saying that the resurrection is past already; and OVERTHROW the faith of some.
Hymenaeus was not content to make shipwreck of his own faith. Now, we find him teaching false doctrine [eschatology] and thereby overthrowing the faith of others. Sounds like he was teaching Preterism.
2 Tim 4:10
10 For Demas hath forsaken me, having loved this present world, and is departed unto Thessalonica; ...
Paul warned Timothy extensively about the lure of materialism. Apparently, many believers had quit and become entangled in the lust for money.
1 Tim 6:10
10 For the love of money is the root of all evil: which while some coveted after, they have erred from the faith, and pierced themselves through with many sorrows.
This brings to mind the parable of the Sower. Remember, some fell among "thorns." Jesus said the "thorns" were the cares of this world and the love of money, which after the seed has sprouted, and begun to grow, they choke the Word, and the plant dies.
These examples of Christians who's faith failed because of a love of money or power demonstrate that the warnings in Scripture about falling away are real.
Here is a conditional promise. Can you tell me what the condition is?
20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
21 For if God spared not the natural branches, take heed lest he also spare not thee.
22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, IF thou continue in his goodness: otherwise thou also shalt be cut off.
That little word "IF", makes a big difference, doesn't it?
Can you point out the condition in this verse?
1 Cor 15:1-2
1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2 By which also ye are saved, IF ye keep in memory what I preached unto you, unless ye have believed in vain.
There's that pesky little word "IF", again.
(Looks like their salvation is linked to perseverance. Kind of like, "he that endures to the end will be saved. Matt 24).
21 And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled
22 In the body of his flesh through death, to present you holy and unblameable and unreproveable in his sight:
23 IF ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel,which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister;
Again, we find this in the Scriptures. Another conditional statement. That little word "IF" messes things up again!!
12 Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.
13 But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin.
14 For we are made partakers of Christ, IF we hold the beginning of our confidence stedfast unto the end;
"IF", once again. There are many of these in the Scriptures. You may want to look them up.
So, I don't know how you explain Scriptures like these away. I'm sure there is an "explanation" somewhere. But it looks like UNBELIEF will surely ruin us. It is afterall, the opposite of FAITH. But what this passage reveals, is that it can happen to a Believer. A hard heart leads to unbelief and unbelief leads to departing from God.
We will be made partakers with Christ IF we hold our initial confidence [or faith] until the end.
1 Therefore we ought to give the more earnest heed to the things which we have heard, lest at any time we should let them slip.
2 For if the word spoken by angels was stedfast, and every transgression and disobedience received a just recompence of reward;
3 How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him;
I'm really surprised that people do not see these conditional statements in the Scriptures. But, I think the man-made doctrines have blinded them and made these scriptures of "no effect".
"Neglect" is treating something that is precious, casually. It is carelessness. Unfortunately, this is the state of many Christians today. Yet, they think they are in no danger. That is because a false Gospel of false security is being preached and the reason why you cannot tell the difference between the world and the church, today.
19 Brethren, if any of you do err from the truth, and one convert him; (Who are the brethren that James is talking to?)
20 Let him know, that he which converteth the sinner from the error of his way shall save a soul from death, and shall hide a multitude of sins.
The only death that does not hide a multitude of sins is eternal death, not physical death. Because after physical death, we will all be judged.
Of course people think up all manner of explanations why people fall away. The main one is that they were never saved to begin with. That does not cohere with the preponderance of scriptures. What I have outlined for you does agree with the preponderance of Scripture and experience. Too many of us have known truly born-again people who have departed from the faith. If your man-made doctrine says that cannot happen, then it is convenient to say, "they were never born-again".