The assurance of salvation: this is basic christian doctrine by the way- something that the earliest christians believed
1John 5:13 These things have I written unto you that believe on the name of the Son of God; that ye may KNOW that ye have eternal life, and that ye may believe on the name of the Son of God.
Eph 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were SEALED with that Holy Spirit of promise,
Eph 1:14 Which is the EARNEST (promise) of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
Col 2:13 And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together WITH him, having FORGIVEN you all trespasses;
Col 2:14 BLOTTING OUT the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross;
Col 2:15 And having spoiled principalities and powers, he made a show of them openly, triumphing over them in it.
John 5:24 Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, HATH (or has) everlasting life, and SHALL NOT come into condemnation; but IS PASSED from death unto life.
John 4:14 But whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into EVERLASTING LIFE.
John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not (will not) perish, but have everlasting life.
Rom 6:22 But now being MADE FREE from sin, and become servants to God, ye have your fruit unto holiness, and the end everlasting life.
John 6:40 And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may (will) have everlasting life: and I WILL raise him up at the last day.
John 6:47 Verily, verily, I say unto you, He that believeth on me HATH (has) everlasting life.
Rom 8:35 Who shall separate us from the love of Christ? shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword?
Rom 8:36 As it is written, For thy sake we are killed all the day long; we are accounted as sheep for the slaughter.
Rom 8:37 Nay, in all these things we are more than conquerors through him that loved us.
Rom 8:38 For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come,
Rom 8:39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.
John 6:54 Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I WILL raise him up at the last day.
John 10:28 And I give unto them eternal life; and they shall NEVER perish, neither shall any man pluck them out of my hand.
Rom 6:23 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
Eph 2:5 Even when we were dead in sins, hath quickened us together with Christ, by (grace ye are saved
Eph 2:8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
Eph 2:9 Not of works, lest any man should boast.
So..
Syrude.. if you have accepted Christ.. He has forgiven you, and you have eternal life.. because He has sealed you with the Holy Spirit.. and promises you eternal life.
Also.. Matthew 12
Jesus is not talking to saved people when He tells them blasphemy won't be forgiven.. He talked to scribes and pharisees who were denying who He was and His salvation
This does not apply to saved people! If Jesus is talking to unsaved.. why apply it to saved?
Blasphemy.. is rejecting salvation from Jesus.. denying who He is.. at some stage.. a saved person accepts salvation and that Jesus is God!
As for Revelation 22 18-19
Put that in the context of all the other verses about having eternal life.. and also the context of the chapter surrounding it.. and then see what it really is saying.
Consider that the people 'outside the gates' of the heavenly Jerusalem city.. may still be in heaven.. but not have access to the holy city. Saved.. but did not seek after Jesus.. went their own way.
Consider that the heavenly Jerusalem is the local church of heaven.. and not all of heaven in itself.. given that it is possible to come in and out of the heavenly Jerusalem.
But most of all think about the verses that do talk about eternal life.. those are the primary verses.