John 10:27-29 My sheep hear my voice, and I know them, and they follow me: (28) And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. (29) My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
John 5:24 Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life.
These verses promise those that believe on Jesus that they shall not come into condemnation, they shall never perish, and that they have passed from death to life. If there was anything you could do to lose your salvation, these verses could not be true. You can twist a lot of scriptures in the Bible, but not these. If you ever have doubts about your salvation, these are great verses to have memorized.
The Bible also says that we are justified from all things and that our sins have been removed as far as the east is from the west.
Acts 13:39 And by him all that believe are justified from all things, from which ye could not be justified by the law of Moses.
Psalms 103:12 As far as the east is from the west, so far hath he removed our transgressions from us.
Matthew 12:22-33 Then was brought unto him one possessed with a devil, blind, and dumb: and he healed him, insomuch that the blind and dumb both spake and saw.
(23) And all the people were amazed, and said, Is not this the son of David?
(24) But when the Pharisees heard it, they said, This fellow doth not cast out devils, but by Beelzebub the prince of the devils.
(25) And Jesus knew their thoughts, and said unto them, Every kingdom divided against itself is brought to desolation; and every city or house divided against itself shall not stand:
(26) And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand?
(27) And if I by Beelzebub cast out devils, by whom do your children cast them out? therefore they shall be your judges.
(28) But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.
(29) Or else how can one enter into a strong man's house, and spoil his goods, except he first bind the strong man? and then he will spoil his house.
(30) He that is not with me is against me; and he that gathereth not with me scattereth abroad.
(31) Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
(32) And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
(33) Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit.
Get the context of what is going on here. The Pharisees see Jesus casting out devils and accuse him of casting out devils by Beelzebub. Jesus basically tells them it's ridiculous to think Satan is casting out Satan, and tells them they had just gone too far. They blasphemed the Holy Ghost, and were never going to be forgiven. This account is in 3 of the 4 gospels, and the account in Mark makes it clear he said that because they said he had an unclean spirit. (Mark 3:30) You can, in fact, go too far and be beyond forgiveness if you are an unsaved person, reject Christ and blaspheme the Holy Ghost. However, you will also notice that none of the Pharisees repented, that is changed their mind about what they said. None of them asked to be forgiven. This is explained for us in John 12
John 12:37-40 But though he had done so many miracles before them, yet they believed not on him:
(38) That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed?
(39) Therefore they could not believe, because that Esaias said again,
(40) He hath blinded their eyes, and hardened their heart; that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them.
John 3:18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
Notice it says that those who don't believe are condemned already because they have not believed. In other words they never believed on the Son of God. People who have committed the unpardonable sin are not capable of believing on the Son of God, and in most cases aren't too worried about it. If you are reading this thinking you might have committed the unpardonable sin, if you believe the gospel, you haven't. If you aren't saved and are worried, get saved now before it's too late. Someday it will be too late for everyone who does not believe the gospel. Whether that is when they die, or while they yet live with a hardened heart. That is why the Bible says NOW is the accepted time.
2Cor. 6:2 (For he saith, I have heard thee in a time accepted, and in the day of salvation have I succoured thee: behold, now is the accepted time; behold, now is the day of salvation.)