Unpardonable sin?

What does it mean to sin against the Holy Spirit?
 
Here are some verses which may be pertinent:
 
EX 23:20-21 "See, I am sending an angel ahead of you to guard you along the way and to bring you to the place I have prepared. Pay attention to him and listen to what he says. Do not rebel against him; he will not forgive your rebellion, since my Name is in him."
 
JOS 24:19 Joshua said to the people, "You are not able to serve the Lord. He is a holy God; he is a jealous God. He will not forgive your rebellion and your sins."
 
MT 6:15 "But if you do not forgive men their sins, your Father will not forgive your sins."
 
So from these verses, it seems that rebelliousness, refusal to submit to God, is the unforgiveable sin. And this is not done in a moment, one sinful deed does not seem to be what is meant:
 
HEB 10:26 "If we deliberately keep on sinning after we have received the knowledge of the truth, no sacrifice for sins is left..."
 
So no one sin seems to be the unpardonable sin per se, rather an attitude of resistance, of refusing the light, as in the Pharisee's response to Jesus:
 
Matthew 12:24  But when the Pharisees heard this, they said, "It is only by Beelzebub, the prince of demons, that this fellow drives out demons."
 
To sin against the light of the very arm of God openly at work would be to approach this sin, as we may very well see in the example of the devil:
 
Ezekiel 28:14-15  You were anointed as a guardian cherub, for so I ordained you. You were on the holy mount of God; you walked among the fiery stones. You were blameless in your ways from the day you were created till wickedness was found in you.
 
To sin in the very inmost presence of God would be to sin in this way.

For those who are concerned that they may have committed the unpardonable sin:
 
"Be not discouraged at broken and spilled resolutions; but to it, and to it again!"
 
"Say 'I will not pass from my claim: suppose Christ should pass from His claim to me, I shall not go back upon my side. Howbeit my love to Him be [small], yet Christ shall have it, such as it is.' Say, 'I shall rather spill twenty prayers, than not pray at all. Let my broken words go up to heaven: when they come up into the Great Angel's golden censer, that compassionate Advocate will put together my broken prayers, and perfume them.' "
 
" 'Oh,' say ye, 'I am slain with hardness of heart, and troubled with confused and melancholious thoughts.' Answer--My dear brother, what would you conclude thence? Down in Christ's hospital, where sick and distempered souls are under cure, it is not [important]. Give Christ time to end His work in your heart. I charge you to make psalms of Christ's praises for His begun work of grace. Make Christ your music and your song; for complaining and feeling of [neediness] does often swallow up your praises. Borrow joy and comfort from the Comforter. Bid the Spirit do His office in you; and remember that faith is one thing and the feeling and notice of faith another."
 
"But alas! dear brother, it is easy for me to speak words and syllables of peace. There is but one Creator, ye know. Oh that ye may get a letter of peace sent to you from heaven!" (Samuel Rutherford, "Letters")
 
"No amount of falls will really undo us if we keep on picking ourselves up each time. We shall of course be very muddy and tattered children by the time we reach home. But the bathrooms are all ready, the towels put out, and the clean clothes in the airing cupboard. The only fatal thing is to lose one's temper and give it up. It is when we notice the dirt that God is most present in us: it is the very sign of His presence..." (Letters of C.S. Lewis, 20 Jan. 1942)
 
And if "every sin and blasphemy will be forgiven men" (Mt. 12:31), and since Paul was both blasphemous, and "the worst of sinners," and yet forgiven (1 Tim. 1:13-16, Paul would then be worse than any blasphemer), we may have reason here to hope that no one will ever actually commit the unpardonable sin.