Jesus appears to contradict Himself. In Luke 12:8-9, He demands that we openly confess Him without hypocrisy, but in verse 10, He says our speech against Him can be forgiven. Yet, God will not forgive speaking against the Spirit. Why? One who blasphemes God's Spirit so thoroughly rejects its power to work in him that he refuses to submit to God. Too proud and rebellious to repent, he cannot be forgiven. A true Christian, though, constantly depends on the Spirit to reflect Christ's life as much as possible.
Christ's sacrifice for the overall forgiveness of sin and the receiving of God's Holy Spirit applies only once for each person, and if an individual rejects God's grace, it cannot be applied again (Hebrews 6:4-6; 10:26-27). This is why apostasy is so serious a matter and why the first-century apostles contended so fiercely against heresy. Eternal lives are at stake!
Sustained neglect can also lead to eternal death. The sinner may know he should repent of his sins, but through lethargy, he never bothers to overcome them. In his apathy, he may try to appear righteous, but he is not fooling God. In effect, he is blaspheming God's Spirit by refusing to repent, so his sin is unpardonable.