Thank you for that comprehensive answer regarding blasphemy. That makes a lot of sense. I see what you mean about seeing a miracle and still rejecting God. Does that mean no one could commit blasphemy against the Holy Spirit today unless they had a near-death experience or something like that? So just saying or thinking "I blaspheme," would not be enough to commit this sin? Also, Jesus says blasphemy against himself could be forgiven. What does that mean? Lots of questions.
Recall that from Numbers 15:30-31 we learn that God's definition of blaspheme is acting in defiance of the Lord and His commandments or willfully sinning when you know full well that it is wrong. While miraculous gifts have ended (I Corinthians 13:8-13), it doesn't mean that the Holy Spirit has no involvement in this world today. "For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame" (Hebrews 6:4-6).
The Bible that you and I read is the work of the Holy Spirit. "knowing this first, that no prophecy of Scripture is of any private interpretation, for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit" (II Peter 1:20-21). Thus, if a person totally rejects the Bible, despite seeing and understanding that it must be the product of God, there is nothing I or anyone else can do for such a person because it is by that very word that a person is saved (Romans 1:16). What argument could I offer a person who once had accepted it, but now completely rejects it?
Similarly, there are people who, despite the evidence, claim the Bible is the product of man and miracles recorded therein are either myths or misunderstanding of the actual events. When a person makes such claims after having previously accepting those same miracles, then there is nothing left to offer such a person to inspire faith in God because the very evidence of God's trustworthiness is rejected. You cannot talk about what God wants them to do because the words are seen as the changeable words of men.
"Partakers of the Holy Spirit" also has another meaning, the Holy Spirit is involved in our salvation. "Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit" (Acts 2:38). Paul also speaks of this when he wrote, "In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise, who is the guarantee of our inheritance until the redemption of the purchased possession, to the praise of His glory" (Ephesians 1:13-14). The Holy Spirit is our down-payment or guarantee of future salvation. He has demonstrated His trustworthiness in the book He caused to be written. He showed the power of God through the miracles that supported the words being spoken and written. Thus when a person completely and purposely rejects the gift of salvation guaranteed by the Spirit, they are turning their backs on the Holy Spirit and blaspheming His efforts.
<Again, we are not talking about a person who messed up and fell under the sway of Satan, or who allowed Satan to place doubts in their hearts. We are talking about a person who had accepted the Spirit's gift of salvation but then deliberately chose to leave, knowing that what he was doing was wrong, but he decided to reject the Spirit and His works anyway.
Therefore, yes, it can and does happen today.
Blasphemy against Jesus, if unrepented of, can lead a person to Hell just as blaspheming the Spirit, but here a person has rejected Jesus, but hasn't rejected the Bible. It could be a Jew who accepts the Old Testament but refuses to accept Jesus as the Messiah. It could be a Muslim who roughly accepts the Bible but only sees Jesus as a great prophet and nothing more. Such a person could, in theory, still be persuaded out of their false beliefs because there is still common ground from which to work. There is still an acceptance of the Bible, even if it is only in part.
You said, "Again, we are not talking about a person who messed up and fell under the sway of Satan, or who allowed Satan to place doubts in their hearts. We are talking about a person who had accepted the Spirit's gift of salvation but then deliberately chose to leave, knowing that what he was doing was wrong, but he decided to reject the Spirit and His works anyway."
What would happen if this person asked forgiveness? Would he still be condemned to hell, since this is an unforgivable sin?
You are looking at the situation backward. It is not that God is unwilling to forgive anyone's sin or refusing to grant salvation. "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (II Peter 3:9). The problem is that a person who blasphemes the Spirit is not going to choose to repent, and God acknowledges that the problem exists. The very nature of this particular sin is that the blasphemer has closed off the one path that can lead him back to God. God would like to forgive all people, but some people are just not soft-hearted enough to come back to Him.
If you want to be forgiven and are willing to come to God on His terms, then you have not gone so far as to blaspheme the Holy Spirit. The very fact that we are having this conversation tells me that is true because a blasphemer won't care.
For a list of what God asks of men to do before He graciously gives us salvation See: Things that Accompany Salvation.