Hebrews 10:26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
The nature of God is that he is merciful and gracious, forgiving iniquity, transgression and sin, but at the same time he will not clear the guilty.
Exodus 34:6 And the LORD passed by before him, and proclaimed, The LORD, The LORD God, merciful and gracious, longsuffering, and abundant in goodness and truth, 7 Keeping mercy for thousands, forgiving iniquity and transgression and sin, and that will by no means clear the guilty…
In one sense we are all guilty because we all sin but the meaning here is guilty of what is called presumptuous sin.
Psalms 19:13 Keep back thy servant also from presumptuous sins; let them not have dominion over me: then shall I be upright, and I shall be innocent from the great transgression.
The idea in Hebrews 10:26 is that of being determined to deliberately live a life of sin in opposition to the mercy of God. The Bible teaches us that when we understand and believe the gospel we are to respond by repenting of our sinful way of life and being baptised by immersion in water for the remission of our past sins.
Mark 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature. 16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
Acts 2:38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins…
Acts 22:16 And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
1 Peter 3:21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
When we rise from the waters of baptism we begin a new life, living by the commandments of Christ.
Romans 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
Sins that we commit after baptism can be forgiven by repentance and confession in prayer.
1 John 1:7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin. 8 If we say that we have no sin, we deceive ourselves, and the truth is not in us. 9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. 10 If we say that we have not sinned, we make him a liar, and his word is not in us.
The way that God deals with sinners is explained through Ezekiel
Ezekiel 18:21 But if the wicked will turn from all his sins that he hath committed, and keep all my statutes, and do that which is lawful and right, he shall surely live, he shall not die. 22 All his transgressions that he hath committed, they shall not be mentioned unto him: in his righteousness that he hath done he shall live. 23 Have I any pleasure at all that the wicked should die? saith the Lord GOD: and not that he should return from his ways, and live? 24 But when the righteous turneth away from his righteousness, and committeth iniquity, and doeth according to all the abominations that the wicked man doeth, shall he live? All his righteousness that he hath done shall not be mentioned: in his trespass that he hath trespassed, and in his sin that he hath sinned, in them shall he die. 25 Yet ye say, The way of the Lord is not equal. Hear now, O house of Israel; Is not my way equal? are not your ways unequal? 26 When a righteous man turneth away from his righteousness, and committeth iniquity, and dieth in them; for his iniquity that he hath done shall he die. 27 Again, when the wicked man turneth away from his wickedness that he hath committed, and doeth that which is lawful and right, he shall save his soul alive. 28 Because he considereth, and turneth away from all his transgressions that he hath committed, he shall surely live, he shall not die.
Ezekiel 33:11 Say unto them, As I live, saith the Lord GOD, I have no pleasure in the death of the wicked; but that the wicked turn from his way and live: turn ye, turn ye from your evil ways; for why will ye die, O house of Israel?
God takes no pleasure in the death of the wicked. He wants all to turn from wickedness.
2 Peter 3:9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
The parable of the prodigal son teaches us that when we come to our senses and turn back to God he is ready to accept us.
Luke 15:17 And when he came to himself, he said, How many hired servants of my father’s have bread enough and to spare, and I perish with hunger! 18 I will arise and go to my father, and will say unto him, Father, I have sinned against heaven, and before thee, 19 And am no more worthy to be called thy son: make me as one of thy hired servants. 20 And he arose, and came to his father. But when he was yet a great way off, his father saw him, and had compassion, and ran, and fell on his neck, and kissed him. 21 And the son said unto him, Father, I have sinned against heaven, and in thy sight, and am no more worthy to be called thy son. 22 But the father said to his servants, Bring forth the best robe, and put it on him; and put a ring on his hand, and shoes on his feet: 23 And bring hither the fatted calf, and kill it; and let us eat, and be merry: 24 For this my son was dead, and is alive again; he was lost, and is found.
Similarly, the parable of the lost sheep and the lost coin. (see Luke 15:4-10)
There is a proverb in Ecclesiastes 9:4 For to him that is joined to all the living there is hope: for a living dog is better than a dead lion.
While we have life we have the opportunity to turn back to God and he will have mercy upon us.
2 Corinthians 6:17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you,
If we turn our backs on God and the gospel of his son, and choose to live a life of sin, there is nowhere else we can go for salvation.
We will reap what we sow.
Galatians 6:7 Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap. 8 For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting.
When you were ‘saved’ as you put it, were you baptised into Christ for the remission of your sins? If you were, then you can be restored to fellowship with God by repentance and confession in prayer. If you were not baptised, your understanding of the gospel was incomplete and you are not yet ‘in Christ’. Baptism into Christ will wash away your past sins. Either way, Heb 10:26 is not a barrier to your salvation. You still have the opportunity to turn to God, obey the gospel and live.
None are ‘saved’ at the point of belief and baptism. We must all ‘work out our salvation’ by obeying the gospel and changing the way that we think and live.
Philippians 2:12 Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling.
Philippians 3:12 Not as though I had already attained, either were already perfect: but I follow after, if that I may apprehend that for which also I am apprehended of Christ Jesus.
1 Corinthians 9:27 But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway.
I hope you have found this helpful.