What is the second commandment of God? The second commandment of God is: Thou shalt not take the name of the Lord thy God in vain.
Thou shalt not take the name of the Lord thy God in vain; for the Lord will not hold him guiltless that shall take the name of the Lord in vain. (Exodus 20:7)
What are we commanded by the second commandment? By the second commandment we are commanded always to speak with reverence of God, of the saints, and of holy things, and to be truthful in taking oaths and faithful to them and to our vows.
Blessed be the name of the Lord both now and forever. From the rising of the sun unto its going down, may the name of the Lord be praised. (Psalm 112:2-3)
Further reading: CCC 2142-2155