This is not complicated.
We are sealed until the day of redemption by the Holy Spirit. If you have the Holy Spirit, there is your seal. We don't want to complicate what seal means. You have the Spirit of God, then bam, your sealed.
We are bought and paid for with a price our body, soul and spirit are not our own. God paid a dear price for us, but not just the saved, for everyone. We have to keep this in mind.
And he is the propitiation for our sins: and
not for ours only, but also for the sins of the whole world. And hereby we do know that we know him, if we keep his commandments.
(
1Jn 2:2-3)
The price was paid for mankind. Bought and paid for, but some don't know him, some do not accept the price paid.
And all things are of God, who hath reconciled us to himself by Jesus Christ, and hath given to us the ministry of reconciliation;
To wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation.
(2Co 5:18-19)
The whole world is not getting trespasses imputed to them. Not accepting Jesus though, means they have to go before God with no advocate and that is not good. God paid for all his creation through the work of Jesus. Some connect by faith through that grace, others do not.
For the promise, that he should be the heir of the world, was not to Abraham, or to his seed,
through the law, but through the righteousness of faith.
(
Rom 4:13)
Those that connect through faith, get their receipt of being sealed by the Holy Spirit. Others, are paid for, but do not get what freely belongs to them. (Unbelief)
If I am saved (Born again with eternal life with God) can I become unsaved?
I won't cover blaspheme of the Holy Spirit, believes commit that all the time and not punished. However, it took your belief in the Lord to get saved, so It would take an equal action to be unsaved. This is not a wake up and find yourself unsaved one morning by a night of drinking and doing dumb things.
You accepted to be bought and paid for, but just like a slave, God won't force you to stick with him. Your free to turn away at anytime if you have full knowledge of what your turning away from.
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, And have tasted the good word of God, and the powers of the world to come, 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 6:4-6)
This person made a choice to follow something else once they have full knowledge of what they were doing.
For
if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. He that despised Moses' law died without mercy under two or three witnesses: 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?
(Heb 10:26-29)
One sin, and what sin? someone that knew the truth, but counted the blood covenant that sanctified an unholy and unworthy thing. In other words, they no longer wanted to be saved still and went after another god, or just plain did not want Jesus.
If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death.
There is a sin unto death: I do not say that he shall pray for it.
(
1Jn 5:16)
Once again, there is ONE sin unto death. Same one Hebrews talked about and John warns about.
Little children,
keep yourselves from idols. Amen.
(1Jn 5:21)
willing to want to leave God, counting the blood covenant unworthy.
love that line