OK, understand that all the truth on any subject is not found in just one passage...
Isa 28:9 Whom shall he teach knowledge? and whom shall he make to understand doctrine? them that are weaned from the milk, and drawn from the breasts.
Isa 28:10 For precept must be upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little:
With that ground rule in place, let's look at another passage...
Heb 10:26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
Heb 10:27 But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries.
Heb 10:28 He that despised Moses' law died without mercy under two or three witnesses:
Heb 10:29 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?
Sinning wilfully is doing despite to the Holy Spirit. What is wilfull sinning? Seems like we want to sin and our will is to sin when we sin. Is every sin wilfully sinning?
1Jn 5:16 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 5:17 All unrighteousness is sin: and there is a sin not unto death.
There are sins that are not unto death. What would that be?
1Jn 2:1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
1Jn 2:2 And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.
Heb 7:25 Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them.
Our Advocate, our High Priest is Jesus Christ. When we go to Him in repentance and seek His intercession for our sins with the Father, we are forgiven. This si a sin that is not unto death, it has been forgiven and once forgiven is gone...
Psa 103:12 As far as the east is from the west, so far hath he removed our transgressions from us.
So what is the unpardonable sin...
Eph 4:22 That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts;
Eph 4:23 And be renewed in the spirit of your mind;
We do this by going to God and seeking Him, asking for the renewing of our minds...
Rom 12:1 I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.
Rom 12:2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
And presenting ourselves as living sacrifices, willing to do whatever God asks of us.
Eph 4:24 And that ye put on the new man, which after God is created in righteousness and true holiness.
Eph 4:25 Wherefore putting away lying, speak every man truth with his neighbour: for we are members one of another.
Eph 4:26 Be ye angry, and sin not: let not the sun go down upon your wrath:
Eph 4:27 Neither give place to the devil.
Eph 4:28 Let him that stole steal no more: but rather let him labour, working with his hands the thing which is good, that he may have to give to him that needeth.
Eph 4:29 Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
Eph 4:30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
Eph 4:31 Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:
Eph 4:32 And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.
We can grieve the Holy Spirit by continuing in these evil practices without remorse or desire to stop. This is wilfull sinning. Doing as we please without trying to change, whithout trying to do this...
Joh 8:11 She said, No man, Lord. And Jesus said unto her, Neither do I condemn thee: go, and sin no more.
Wilfull sin is simply going the way of the Devil, our own human nature and the way of the world without thought of going God's way or even caring. A very cogent comment was made to me many years ago, "If you are owrried that you have committed the unpardonable sin, you most likely have not."
