Blasphemy is speaking or writing in a way that shows disrespect or insults God. It can also include actions that show contempt toward God. More generally, "blasphemy" can refer to insulting or damaging someone's reputation. This includes any words or actions that degrade or devalue another person. In ancient Greek writings, people used the word "blasphemy" to describe insults or mockery toward both living and dead people. Later, it came to also mean doubting or mocking the power and nature of the gods.
Blasphemy in the Old Testament
In the Old Testament, “blasphemy” always means to insult God, either by attacking him directly or mocking him indirectly. Either way, the glory and honor of God are lessened. So, blasphemy is the opposite of praise. An Israelite might directly insult the “Name” (the personal name of God, Yahweh) by cursing God (Leviticus 24:10–16) or deliberately disobeying God’s law (Numbers 15:30). Either of those blasphemies was punishable by death, as was idolatry, the ultimate blasphemy (Isaiah 66:3).
It was thought that Gentiles, who had never experienced the power and majesty of the Lord, were the most likely blasphemers. Thus the king of Assyria blasphemed in equating the Lord with the gods of the nations he had already conquered (2 Kings 19:4–6, 22). For his arrogance, the king was doomed by the word of the prophet Isaiah. God was also mocked when:
Israel was exiled (Isaiah 52:5);
Edom derided the desolate “mountains of Israel” (Ezekiel 35:12, King James Version); and
The enemy scoffed that God had not protected Jerusalem (Psalm 74:18; 1 Maccabees 2:6).
Blasphemy in the New Testament
In the New Testament, blasphemy takes on the wider Greek meaning. It includes slandering a human being, as well as God (Matthew 15:19; see also Romans 3:8; 1 Corinthians 10:30; Ephesians 4:31; Titus 3:2). It even includes mocking angelic or demonic powers, which is just as wrong as mocking any other being (2 Peter 2:10–12, Jude 1:8–10). In other words, slander, ridicule, and mocking of any kind are totally condemned in the New Testament.
The most common form of blasphemy in the New Testament is blasphemy against God. One might insult God directly (Revelation 13:6; 16:9), mock his word (Titus 2:5), or reject his revelation and its bearer (Acts 6:11). Jesus was accused of blasphemy when he claimed to have a prerogative belonging to God—the power to forgive sins (Mark 2:7). John 10:33–36 reports an attempt to stone Jesus. His accusers said to him, “You, who are a man, declare Yourself to be God” (verse 33). The highest Jewish court (the Sanhedrin) condemned Jesus on the charge of blasphemy because he claimed to be the Son of Man (the Messiah). In their view, Jesus had given no evidence that he was such an exalted personage. Jesus appeared to be mocking the Messiah and, by extension, to mock God himself (Mark 14:64).
The Bible makes clear that blasphemy is forgivable (Matthew 12:32; Mark 3:28–29). But, if a person will not repent, the only remedy is to turn him or her “over to Satan to be taught not to blaspheme” (1 Timothy 1:20).