Matthew 12:31-34 The unpardonable sin

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.³⁴ O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh.

-Matthew 12:31 King James Version (KJV)

Arcana Coelestia, by Emanuel Swedenborg, [1749-56], tr. by John F. Potts [1905-10], at sacred-texts.com

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...[6] Those who have been interiorly infected with spiritual deceit, that is, with hypocrisy, are they who are meant by those who speak against the Holy Spirit, for whom there is no forgiveness, in Matthew: I say unto you, All sin and blasphemy shall be forgiven unto men; but the blasphemy of the spirit shall not be forgiven unto men. Nay, if anyone shall say a word against the Son of man, it shall be forgiven him; but whosoever shall speak against the Holy Spirit, it shall not be forgiven him, neither in this age, nor in that which is to come. Either make the tree good, and its fruit good; or make the tree bad and its fruit bad. O offspring of vipers, how can ye, being evil, speak what is good (Matt. 12:31-34). By "saying a word against the Holy Spirit" is meant to speak well and think evil, and to do well and will evil, respecting those things which are of the Lord, of His kingdom, and of His church, also which are of the Word; for thus falsity lies inwardly hidden in the truths which they speak; and evil, which is hidden poison, in the goods which they do; consequently they are called "an offspring of vipers." [7] In the other life an evil person is allowed to speak evil and also falsity; but not good and truth, because there all are compelled to speak from the heart, and are not allowed to be of a divided mind. They who do otherwise are separated from the rest, and are hidden in hells from which they cannot possibly go forth. That such are they who are meant by "those who say a word against the Holy Spirit" is evident from the above words of the Lord, "Either make the tree good and its fruit good, or make the tree bad, and its fruit bad; how can ye, being evil, speak what is good?" The "Holy Spirit" denotes the Divine truth proceeding from the Lord, thus the Holy Divine Itself, which is thereby interiorly blasphemed and profaned. [8] That it will not be forgiven them is because hypocrisy or deceit in connection with Holy Divine things infects the interiors of man, and destroys everything of spiritual life in him, as was said above, insomuch that at last there is nothing sound in any part of him. For the forgiveness of sins is the separation of evil from good, and the rejection of evil to the sides (n. 8393), which cannot be done with him in whom all good has been destroyed. Therefore it is said "It shall not be forgiven him, neither in this age nor in that which is to come." Of this character also are those who are meant by "him that had not on a wedding garment," who was bound hand and foot and cast out into outer darkness (Matt. 22:11-13, see n. 2132)...

According to the Ascended Master Beloved Saint Germain: "The Holy Ghost, or Holy Spirit, is the feeling side of Life-God-the Activity of Divine Love, or the Mother Expression of Deity. This is why the sin against the Holy Ghost is referred to as that which brings such great distress, because any discord in the feeling breaks the Law of Love, which is the Law of Balance, Harmony, and Perfection. The greatest crime in the Universe against the Law of Love is humanity's almost ceaseless sending forth of every kind of irritable and destructive feeling." ('Unveiled Mysteries' by Godfre Ray King p7-8)