In Mormon theology, the name "Jehovah" (YHWH, Yahweh, the personal name of the God of Israel in the Old Testament) is exclusively the name of the pre-incarnate Jesus Christ. They deny that God the Father is Jehovah. Mormons do not believe in the Biblical Trinity (that there is one and only one God who exists in three distinct persons). They believe that the Father, the Son, and the Holy Spirit are three different divine beings, three distinct gods. The Father, according to Mormonism, is an entirely separate deity from Son. "Jehovah" is the name of the Son, not the Father.
Now, it is true that there is only one Jehovah. The Bible knows of one and only one God in all of existence, and YWHW (Yahweh, Jehovah) is the personal name of that God. It is also true that the New Testament frequently identifies the Son as Jehovah. Problematic for Mormons, however, is the fact that the Bible also identifies the Father and the Spirit as Jehovah. This is perfectly consistent with a Trinitarian perspective that Jehovah is one being who exists in three persons (indeed, it demands that perspective). However, it completely contradicts the Mormon notion that Jehovah is one of many gods and that only the Son, Jesus Christ, is Jehovah. That the Father is also Jehovah is easily demonstrated through a verse in the Old Testament that is part of one of the most frequently cited passages by the New Testament authors:
"The LORD says to my Lord: 'Sit at My right hand Until I make Your enemies a footstool for Your feet,'" (Psalm 110:1).
It is important to note here that, while the English text has the word "Lord" twice, this is actually two different Hebrew words. The first "Lord" is the personal name YHWH (Jehovah). The Second "Lord" is a form of the Hebrew word "adon" which simply means "Master." So, David is saying in this Psalm that "Jehovah says to my Master, sit at my right hand..." Jesus makes it clear that this passage is Messianic:
"Now while the Pharisees were gathered together, Jesus asked them a question: 'What do you think about the Christ, whose son is He?' They said to Him, 'The son of David.' He said to them, 'Then how does David in the Spirit call Him ‘Lord,’ saying, ‘The Lord said to my Lord, “Sit at My right hand, Until I put Your enemies beneath Your feet”’? If David then calls Him ‘Lord,’ how is He his son?” No one was able to answer Him a word, nor did anyone dare from that day on to ask Him another question," (Matthew 22:41-46, see also Mark 12:35-37, Luke 20:41-44).
Jesus point here is that David calls the Messiah his Master, so the Messiah cannot merely be David's son. The Messiah must actually be greater than David to be David's Master. But in saying this, Jesus makes clear that the Messiah is "my Master" to whom Jehovah is speaking. Jehovah, in this passage, refers to the Father who is speaking to the Son, the Messiah, David's Master. Thus, the Name "Jehovah" is applied to the Father. Yet, there is only one Jehovah. Jehovah is a personal name applying only to the one true God of Israel. The Mormon already knows that the Son is Jehovah, but this passage makes it clear that the Father is also Jehovah. In case there is any doubt here, Jesus affirms this interpretation again later at His trial:
"Jesus said to him, 'You have said it yourself; nevertheless I tell you, hereafter you will see the Son of Man sitting at the right hand of Power, and coming on the clouds of heaven,'" (Matthew 26:64, see also Mark 14:62, Luke 22:69).
There is unanimous agreement among scholars that Jesus here puts Psalm 110:1 and Daniel 7 together, proclaiming Himself to be the Son of Man who is enthroned with the Ancient of Days as well as being the "master" who sits at the right hand of Jehovah. Jesus' Apostles also carried on this interpretation. Peter, for example, cites Psalm 110:1 regarding Jesus in his sermon in Acts 2:
"For it was not David who ascended into heaven, but he himself says: ‘The Lord said to my Lord, “Sit at My right hand, Until I make Your enemies a footstool for Your feet,”’ (Acts 2:34-35).
The one who ascended into heaven to sit at the right hand of Jehovah was not David, but rather David's master, the Messiah. Jesus ascended to heaven to sit at the right hand of the Father. The Father is Jehovah. In one of Peter's own letters, he makes this same point, proclaiming the resurrection of Jesus Christ, "who is at the right hand of God, having gone into heaven, after angels and authorities and powers had been subjected to Him," (1 Peter 3:22). The Book of Acts also points to this passage again in the vision of Stephen just before his death:
"But being full of the Holy Spirit, he gazed intently into heaven and saw the glory of God, and Jesus standing at the right hand of God; and he said, 'Behold, I see the heavens opened up and the Son of Man standing at the right hand of God,'” (Acts 7:55-56).
All of this is alluding to Jesus as the "my Master" figure at the right hand of Jehovah (the Father) in Psalm 110:1. The Book of Hebrews makes the same point yet again. In the first chapter, a number of passages are cited to show the divinity of Jesus and His unique superiority over even the heavenly angels. These are presented as God the Father speaking to (or about) the Son. For example, it says:
"For to which of the angels did He ever say, 'You are My Son, Today I have begotten You'? And again, 'I will be a Father to Him And He shall be a Son to Me'?" (Hebrews 1:5).
It is in this context, the Father speaking to the Son, that we read:
"But to which of the angels has He ever said, 'Sit at My right hand, Until I make Your enemies A footstool for Your feet'?" (Hebrews 1:13).
The Father (Jehovah) says to the Son (my master), "sit at my right hand..." etc. The same identification is made later in the book:
"Every priest stands daily ministering and offering time after time the same sacrifices, which can never take away sins; but He [Jesus], having offered one sacrifice for sins for all time, sat down at the right hand of God, waiting from that time onward until His enemies be made a footstool for His feet," (Hebrews 10:11-13).
Again, the Father is the one speaking in Psalm 110:1 (Jehovah) the Son is the one addressed (David's Master). The Father is identified as Jehovah. The Book of Hebrews continues to draw on this Psalm in this precise manner. For example, Psalm 110:4 says:
"The LORD (YHWH, Jehovah) has sworn and will not change His mind, 'You are a priest forever According to the order of Melchizedek,'"
Jehovah is swearing to the person that David calls "my Lord/Master" that they are a priest forever according to the order of Melchizedek. The author of the Book of Hebrews expounds:
"So also Christ did not glorify Himself so as to become a high priest, but He who said to Him, 'You are My Son, Today I have begotten You'; just as He says also in another passage, 'You are a priest forever According to the order of Melchizedek,'” (Hebrews 5:5-6).
"Jesus has entered as a forerunner for us, having become a high priest forever according to the order of Melchizedek," (Hebrews 6:20).
Very clearly here, the Father says to the Son, "You are a priest forever..." The Father is Jehovah. The Father is not the Son. They are two distinct and interactive persons. Yet they are both Jehovah, and there is only one, individual being whose name is Jehovah. One God, one being, who exists as multiple persons. This is the God of the Bible and the God of historic Christianity, not the god of Mormonism.