Jesus said in Matthew,
All power has been given to me in heaven and on earth. Go forth, therefore, and make disciples of all the nations, baptizing them in the name of the Father, the Son, and the Holy Spirit, teaching them to observe all things that I have commanded you; and behold, I am with you all the days, even to the close of the age. (Matthew 28:18, 19, 20)
Up to this point I have shown that the Divine Being called the Father and the Divine Being called the Son are one in the Lord. I therefore need now to show that the Holy Spirit is the same as the Lord.
The reason the Lord said that they were to baptize in the name of the Father, the Son, and the Holy Spirit is that there is a threeness or trinity in the Lord. There is the divine nature that is called the Father, the divine human nature that is called the Son, and the emanating divine nature that is called the Holy Spirit. The divine nature that is the Father and the divine nature that is the Son is the divine nature as the source, while the emanating divine nature that is the Holy Spirit is the divine nature as means.
In the booklets Divine Providence and Omnipotence, Omnipresence, and Omniscience, you will see more on the point that the only divine nature that emanates from the Lord is the divine nature that is he himself—it is a matter that takes more than a few words to explain.
We can illustrate this threeness in the Lord by comparison with angels. They have souls and bodies and also emanations that radiate from them, emanations that are their own selves extending beyond themselves. I have been granted an abundance of knowledge about this emanation, but this is not the place to present it.
After death, everyone who turns to God is first taught by angels that the Holy Spirit is none other than the Lord and that “going forth” and “emanating” is nothing but enlightening and teaching by means of presence, a presence that depends on our acceptance of the Lord. So after death, many people leave behind the concept of the Holy Spirit that they had formed in the world and accept the idea that it is the Lord’s presence with us through angels and spirits, a presence from and by means of which people are enlightened and taught.
Then too, it is common practice in the Word to name two divine beings, sometimes three, who are nevertheless one, such as Jehovah and God, Jehovah and the Holy One of Israel, Jehovah and the Mighty One of Jacob, as well as God and the Lamb; and because they are one it says elsewhere that Jehovah alone is God, Jehovah alone is the Holy One and is the Holy One of Israel, and there is no God other than him. Sometimes God is called the Lamb and sometimes the Lamb is called God, the latter in the Book of Revelation and the former in the prophets.
We can see that it is the Lord alone who is meant by “the Father, the Son, and the Holy Spirit” in Matthew 28:19 from what precedes and follows that verse. In the preceding verse the Lord says, “All power has been given to me in heaven and on earth,” and in the next verse the Lord says, “Behold, I am with you all the days, even to the close of the age.” So he is talking about himself alone, saying this so that they would know that the trinity was in him.
To make it known that the Holy Spirit is no divine thing other than the Lord himself, I need to show what “spirit” means in the Word.
1. “Spirit,” in a broad sense, refers to an individual’s life.
2. Since our life varies depending on our state, “spirit” means the variable attitude we take toward life.
3. It also means the life of those who have been regenerated, which is called spiritual life.
4. Where “spirit” is used in speaking of the Lord, though, it means his divine life and therefore the Lord himself.
5. Specifically, it means the life his wisdom gives us, which is called divine truth.
6. Jehovah himself—that is, the Lord—spoke the Word through prophets.
from The Lord, Section 46