What about Hebrews 10:26-31
For if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, but a fearful expectation of judgment, and a fury of fire that will consume the adversaries. Anyone who has set aside the law of Moses dies without mercy on the evidence of two or three witnesses. How much worse punishment, do you think, will be deserved by the one who has spurned the Son of God, and has profaned the blood of the covenant by which he was sanctified, and has outraged the Spirit of grace? For we know him who said, "Vengeance is mine; I will repay." And again, "The Lord will judge his people." It is a fearful thing to fall into the hands of the living God.
If you believe Paul wrote Hebrews, notice how he includes himself in the warning " if "we" go on sinning"
Hebrews 6:4-6New International Version (NIV)
4 It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, 5 who have tasted the goodness of the word of God and the powers of the coming age 6 and who have fallen away, to be brought back to repentance. To their loss they are crucifying the Son of God all over again and subjecting him to public disgrace.
Also Peter speaks of the dog that returns to it's vomit. It would have been better for that person to not have known the way than to forsake the holy commandment given to him. You also have passages which talk about how people in the church where trying to bring in a false doctrine of grace as a license to sin. I've been struggling with these passages for the past 3 months. Anybody who is in sin and knows it, REPENT, and ask God Jehovah to forgive, make your paths strait, and keep you in His hand. It's not worth the terror of believing you lost your salvation. True saving faith as opposed to intellectual faith, is going to make you want to walk in obedience. Also, the scripture where Paul warns believers to work out their salvation in trembling and fear, he talks about the branches being removed from the vine for not producing fruit. I pray every day it's not too late to repent for myself. Don't chance sin, sin is nothing more than an illusion. NOTHING in this life matters but a relationship with God through Christ!