As FrMattCH says....
If you reject Christ, then how can you be forgiven your sins?
Nothing else can pay for them or forgive them.
To reject Christ is to reject eternal pardon.
If you do this, then you have rejected the only way (John 14:6) to be forgiven, thus this is the one and only sin you can commit whereby you cant receive forgiveness, as you have rejected the only means available to be forgiven.
So, the one sin you can commit that will keep you unforgiven and unsaved and lost, is to reject forgiveness which is to reject Jesus Christ and remain a Christ rejector until you die....
See it?
So this is the sin of dying unpardoned and is the one and only sin you can commit that cant be covered by Jesus's sacrifice, as you have rejected Jesus's sacrifice..
And regarding blasphemy of the Holy Spirit.
This is one of those verses that Christians needlessly fear, as they think it ither means to say the term God D_ _ _, or they think it means to somehow anger or offend the HS, perhaps by... "living in sin after you are saved"..
Well, let me tell you what it actually is..
1st, you as a Christian cant commit this sin.
And the reason is, you are not a 1st Century Pharisee who is attributing the healing power of Christ to the devil.
So, if you want to commit it, here is how you do it.
Get in a time machine.
Go back 2000+ years to the time of Christ.
Become a Christ rejecting Pharisee.
Then,..
Find Jesus healing someone, and then say to the crowd standing by who are astonished that Jesus just miraculously healed someone, that He was able to do this by... "the power of Satan".
So, what you have done, is you have tried to keep the people who would believe on Christ from believing on him by attributing his work to the Devil.
In other words you are a Pharisee watching Jesus , who is so full of envy that you are trying to discredit the work of the Holy Spirit as Christ is doing it, by saying these miracles are the "work of Satan's power".
The idea being,... to keep the Jew who were watching from accepting Christ as their Messiah.
So, to BLSPHMY the HS, is to become a 1st Century Pharisee who is literally trying to created a VERBAL ROADBLOCK of DOUBT and UNBELIEF between Jesus and anyone who would come to him after watching him do a miracle .
Literally, it means to be a Pharisee who is trying to convince the Jews that Jesus is not their Messiah, by attributing Jesus's miracles to the devil.
Now after reading what i just told you, go and read Matt 12:22-32 where Jesus is warning the Pharisees who are standing there not to blasphemy the Holy Spirit.
You'll see it, if you've not seen it before.
And the other part of this, so that you have crystal clarity and are never again bugged by this verse, is to remember what the only sin is you can commit that will keep you unforgiven.
Remember?
Its to reject Christ, and by doing that you have rejected pardon.
Now, go back and apply this realization to the Pharisees minds and hearts.
Apply it like this......."Pharisee, if your heart rejects Christ, then THIS IS WHY you are blaspheming the Holy Spirit, and because your heart is like that, you cant be forgiven.... as you are a CHRIST REJECTOR"...
see it?
be blessed,
K