Heidelberg Catechism · 1563

Q100. Is the blaspheming of God's Name by swearing and cursing such a grievous sin that God is angry also with those who do not prevent and forbid it as much as they can?

Certainly, for no sin is greater or provokes God's wrath more than the blaspheming of His Name. That is why He commanded it to be punished with death.
Answer · Heidelberg Catechism

Scripture proofs

  1. [1]
    Leviticus 5:1

    And if a soul sin, and hear the voice of swearing, and is a witness, whether he hath seen or known of it; if he do not utter it, then he shall bear his iniquity.

  2. [2]
    Leviticus 24:16

    And he that blasphemeth the name of the Lord, he shall surely be put to death, and all the congregation shall certainly stone him: as well the stranger, as he that is born in the land, when he blasphemeth the name of the Lord, shall be put to death.

Proof texts as given in the original; verse text from the King James Version.