Who was speaking to Moses as recorded in the Book of Moses.
Thank you for your question as I feel the answer to it is one that each member of the Church could benefit from knowing. Studying this answer may greatly provide a deeper and richer understanding of the scriptures as well as our relationship with the Savior and our Father in Heaven.
While Moses does speak briefly with Satan:
“…Satan came tempting him, saying: Moses, son of man, worship me.” Moses 1:12
The majority of the conversations held in the Book of Moses are between Moses and “God”. I believe your question ultimately revolves around, “Who exactly is God in the Book of Moses?”. As we understand who is speaking to Moses in the Pearl of Great Price, we then better understand who is actually speaking in other parts of the standard works as well. In Moses 1:1-3 we read:
1 The words of God, which he spake unto Moses at a time when Moses was caught up into an exceedingly high mountain,
2 And he saw God face to face, and he talked with him, and the glory of God was upon Moses; therefore Moses could endure his presence.
3 And God spake unto Moses,
It is a very common and understandable misconception that Moses is in fact speaking with God the Father or Our Father in Heaven. While this is a common misconception, the reality is Moses is in fact speaking with the Savior or Jesus Christ instead. Many who read the Book of Moses naturally assume that by using the word “God” that it must mean God the Father. This misconception is often further reinforced by reading later in Moses 1:4 where “God” says:
And, behold, thou art my son; …
So, how does Jesus Christ then claim that Moses is his son? Isn’t Moses the son of Our Father in Heaven? Isn’t Moses instead the ‘brother’ of the Jesus Christ?
As we read the scriptures it is important to understand the concept of ‘Divine Investiture’ or ‘Divine investiture of Authority’. For help with this concept we turn to The Pearl of Great Price Student Manual – The Book of Moses where is says:
Moses 1:3–8. Who Spoke to Moses?
The personage who spoke to Moses was the premortal Jesus Christ, who is Jehovah, the God of the Old Testament. Being one with Heavenly Father, Jesus at times speaks as if He were God the Father (see Moses 1:6). This is known as divine investiture, whereby Christ is invested with authority to speak for and in behalf of the Father
The Savior is invested/given authority to speak as though he is God the Father. A modern day secular example of this might be a ‘Power of Attorney’. A Power of Attorney is a legal document you sign granting authority to someone else you trust to both act and make decisions on your behalf as if they you were actually there. In your absence, the individual to whom you have given Power of Attorney works on your behalf and in your best interest. President Joseph Fielding Smith shed additional light on this subject:
“All revelation since the fall has come through Jesus Christ, who is the Jehovah of the Old Testament. … He is the God of Israel, the Holy One of Israel; the one who led that nation out of Egyptian bondage, and who gave and fulfilled the Law of Moses. The Father has never dealt with man directly and personally since the fall, and he has never appeared except to introduce and bear record of the Son.” Doctrines of Salvation, 1:27
17 It no sooner appeared than I found myself delivered from the enemy which held me bound. When the light rested upon me I saw two Personages, whose brightness and glory defy all description, standing above me in the air. One of them spake unto me, calling me by name and said, pointing to the other—This is My Beloved Son. Hear Him!
6 And behold, the third time they did understand the voice which they heard; and it said unto them:
7 Behold my Beloved Son, in whom I am well pleased, in whom I have glorified my name—hear ye him.
And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
Thank you again for your question Patrick. Moving forward, I hope that when you and others read the scriptures you may better understand the dynamics between us, The Savior and Our Father in Heaven. Below is an excellent video of the conversation between Moses and Jesus Christ.