You Are Not to Take the Name of Jehovah Your God in Vain, Because Jehovah Will Not Hold Guiltless Someone Who Takes His Name in Vain
In the heavenly meaning, taking the Lord’s name in vain parallels what the Lord said to the Pharisees:
All sin and blasphemy is forgiven people, but blasphemy of the Spirit is not forgiven. (Matthew 12:31-32)
“Blasphemy of the Spirit” means blasphemy against the divinity of the Lord’s human manifestation and against the holiness of the Word.
In the highest or heavenly meaning, the “names of Jehovah God” stands for the Lord’s divine-human manifestation, as the following passages make clear:
Jesus said, “Father, glorify your name.” And a voice came out of heaven that said, “I both have glorified it and will glorify it again.” (John 12:27-28)
whatever you ask in my name, I will do it, so that the Father is glorified in the Son. If you ask anything in my name, I will do it. (John 14:13-14)
In the heavenly sense the phrase in the Lord’s prayer “Your name must be kept holy” [Matthew 6:9] has the same meaning, as does the word “name” in Exodus 23:21 and Isaiah 63:16.
Since Matthew 12:31 and 32 says that “blasphemy of the Spirit” is not forgiven us, and this is what the heavenly meaning refers to, for this reason the following phrase is added to this commandment: “because Jehovah will not hold guiltless someone who takes his name in vain.”
from True Christianity, Section 299
Secrets of Heaven 