Key Text
31Wherefore 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. 32And 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. (Matthew 12:31-32, KJV; cf. Mark 3:28-29)
What is "Blasphemy"?
While you may not be asking what blasphemy means, clear definitions are important to a proper understanding of the question and its answer. According to our modern dictionary, "blasphemy" is given as:
blasphemy | ˈblasfəmē |
noun (plural blasphemies)
the act or offense of speaking sacrilegiously about God or sacred things;
profane talk: he was detained on charges of blasphemy | screaming
incomprehensible blasphemies.
The Greek word is defined in Strong's Concordance as:
βλασφημία blasphēmía, blas-fay-me'-ah; from G989; vilification (especially against God):—blasphemy, evil speaking, railing.
Essentially, blasphemy has broad application, and, as used in this answer, entails any form of speaking against God, including undermining His character or misrepresenting Him.
Who is the "Holy Spirit"?
Is the Holy Spirit a "person"? While the Bible may not define "person" or its usage, the Bible is clear as to the fact that God is both holy and a spirit.
Exalt the LORD our God, and worship at his holy hill; for the LORD our
God is holy. (Psalm 99:9, KJV)
God is a Spirit: and they that worship him must worship him in spirit
and in truth. (John 4:24, KJV)
God is both holy and a spirit--a "Holy Spirit." If God is a person, and God is a holy spirit (i.e. the "Holy Spirit" is God), it follows that the Holy Spirit is a person, and to speak against God's holy person is the epitome of "blasphemy."
Throughout the Bible, the Holy Spirit is used with respect to the spirit of God, the spirit of the Father, or the spirit of Christ Jesus, in whom the Father dwelt. Because the Father is a spirit, and that spirit was in Christ, the "holy spirit" represents God's own omnipresence, and is not human but divine.
Who is the "Son of Man"?
Jesus called himself the "son of man."
When Jesus came into the coasts of Caesarea Philippi, he asked his
disciples, saying, Whom do men say that I the Son of man am? (Matthew
16:13, KJV)
This had deep Biblical significance with respect to his identity.
God is not a man, that he should lie; neither the son of man, that he
should repent: hath he said, and shall he not do it? or hath he
spoken, and shall he not make it good? (Numbers 23:19, KJV)
And also the Strength of Israel will not lie nor repent: for he is not
a man, that he should repent. (1 Samuel 15:29, KJV)
What is Jesus Saying?
Jesus said that if one were to speak against the "son of man," it would be forgiven. Since Jesus was himself the "son of man," speaking against Jesus can be forgiven.
But to speak against the Holy Spirit is to speak, not against a mere man, but against God Himself. This, according to Jesus, is not forgiven.
Applications to Trinitarianism / Nontrinitarianism
As shown above, the Bible is clear that God is not a man. It is also clear that Jesus is a man. Anytime that a man speaks as if he were God, this is reckoned as blasphemy. The Jews, for example, accused Jesus of blasphemy for this very reason.
32Jesus answered them, Many good works have I shewed you
from my Father; for which of those works do ye stone me?
33The Jews answered him, saying, For a good work we stone
thee not; but for blasphemy; and because that thou, being a man,
makest thyself God. (John 10:32-33, KJV)
The Jews were looking at Jesus' humanity, not recognizing the Divinity within him, which was speaking through him. When Jesus forgave sins, for example, it was not his humanity speaking--but the Spirit of God within him who gave him the words.
It is blasphemy for a man to speak as God. But Jesus did not do this. He spoke for God, not as if he were himself God. He never claimed to be God. He stated plainly that he spoke the Father's words, because the Father dwelt in him.
For I have not spoken of myself; but the Father which sent me, he gave
me a commandment, what I should say, and what I should speak. (John
12:49, KJV)
Believest thou not that I am in the Father, and the Father in me? the
words that I speak unto you I speak not of myself: but the Father that
dwelleth in me, he doeth the works. (John 14:10, KJV)
If it is blasphemy for a man to say he is God, or to attempt to speak as if he were God, it is also blasphemy to speak as if another man were God. To call any man God, when God says He is not a man, is blasphemy.
"God the Son": Trinitarians have a "God the Son" to whom they give homage. This "God" is never mentioned in the Bible. The expression "God the Son" exists nowhere in the scriptures. God says He is not the "son of man"--whereas Jesus, whom Trinitarians call "God the Son," says he is the "son of man." In this, they essentially call God a liar, saying that God is the "son of man" even though God claims otherwise. This is the epitome of blasphemy.
To avoid blasphemy, one must not misrepresent God. God says He is not a man, and that He is not the son of man. If one portrays God as having lied in saying these things, one blasphemes.
"God the Holy Spirit": Further, Jesus taught that the Father is "the only true God" (see John 17:1-3). If one claims that the "Holy Spirit" is another "true God," other than the Father (as Trinitarians believe), then one likewise misrepresents God, and blasphemes.
Nontrinitarians are clear of this blasphemy, because they accept God's words at face value. God says what He means, and He means what He says.