For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies. (Matthew 15:19, NKJV)
The last in this series of sins proceeding from the heart is blasphemies. It means to speak evil of or to rail against (Strong’s Dict.); railing, reviling, “slanderous detraction, speech injurious to another’s good name” (Thayer). Blasphemy is the expression of malice and contempt, and can be directed toward God and toward people (Matthew 12:31-32; Colossians 3:8; 1 Timothy 6:4). The sin of blasphemy is notably applied to “impious and reproachful speech” against God and His divine majesty (cf. Daniel 11:36; Mark 2:7). For example, taking God’s name in vain is surely a form of blasphemy because such cursing impiously slanders God (Exodus 20:7). Like Saul before his conversion, we are blasphemers when we speak against Christ and His gospel (1 Timothy 1:13). This warns us that even when we think we are serving God (as did Saul), we may in fact be blasphemers (Acts 26:9-11; John 16:2). Take extreme care not to speak against the truth of Christ, for to do so is to speak against God Himself (Revelation 2:9). To rail against the Bible is blasphemy against God Himself. Guard your heart so it does not lead your mouth to blasphemy the Father, the Son, the Holy Spirit, and God’s holy word. Speak kindly of men, too (Ephesians 4:31-32). Slanderous reviling reveals a malicious heart that must be put away (James 1:21; 1 Peter 2:1-3).