Jesus identified Himself as “the Son of Man” to set an example for us. The New Covenant is based on Jesus’ blood of forgiveness, which is better than the blood of Abel, Moses, Elisha, etc., which cries for vengeance.
Blasphemy against the Holy Spirit is knowing something as the work of God, and still speaking against it. This is usually done for personal gain, legalism, etc. – e.g., Judas Iscariot, the Pharisees, etc. The proof of such blasphemy is that there is no desire for repentance.
There are 3 aspects of justification: justification by faith (Romans 5:1); justification by our works of faith (James 2:24); and justification by our words of faith (Matthew 12:36-37).
The solution to not speaking careless words is not that we live in constant fear of what we will say, but ensuring that our TREASURE is good. Foul words indicate foul treasure, empty words indicate empty treasure. If our treasure is set on things above, then our deeds and words WILL be good (Colossians 3:1-9).