OT:
a. Plurality of persons
Genesis 1:26 "Then God said, “Let Us make man in Our image, according to Our likeness;"
Genesis 3:22 "Then the Lord God said, “Behold, the man has become like one of Us"
Genesis 11:7 "Come, let Us go down and there confuse their language,"
Psalm 45:6-7 "Your throne, O God, is forever and ever; A scepter of uprightness is the scepter of Your kingdom. You have loved righteousness and hated wickedness; Therefore God, Your God, has anointed You With the oil of joy above Your fellows." (A picture of Jesus)
Isaiah 6:8 'Then I heard the voice of the Lord, saying, “Whom shall I send, and who will go for Us?” Then I said, “Here am I. Send me!”' (Notice that the author uses both singular and plural)
Psalm 110:1'"The Lord says to my Lord: “Sit at My right hand Until I make Your enemies a footstool for Your feet.”' (Clearly an indication of the Messiah to come)
Hosea 1:7 "But I will have compassion on the house of Judah and deliver them by the Lord their God, and will not deliver them by bow, sword, battle, horses or horsemen.”
Malachi 3:1 "Behold, I am going to send My messenger, and he will clear the way before Me. And the Lord, whom you seek, will suddenly come to His temple; and the messenger of the covenant, in whom you delight, behold, He is coming,” says the Lord of hosts."
b. The Holy Spirit as God
Genesis 16:13 "Then the angel of the Lord said to her, “Return to your mistress, and submit yourself to her authority.” Moreover, the angel of the Lord said to her, “I will greatly multiply your descendants so that they will be too many to count...Then she called the name of the Lord who spoke to her, “You are a God who sees”; for she said, “Have I even remained alive here after seeing Him?"
Ex 23:20-22 "Behold, I am going to send an angel before you to guard you along the way and to bring you into the place which I have prepared. 21 Be on your guard before him and obey his voice; do not be rebellious toward him, for he will not pardon your transgression, since My name is in him.."
Numbers 22:35 "But the angel of the Lord said to Balaam, “Go with the men, but you shall speak only the word which I tell you.”
Judges 2:1-2 "Now the angel of the Lord came up from Gilgal to Bochim. And he said, “I brought you up out of Egypt and led you into the land which I have sworn to your fathers; and I said, ‘I will never break My covenant with you, and as for you, you shall make no covenant with the inhabitants of this land; you shall tear down their altars."
Judges 6:11, 14 "Then the angel of the Lord came and sat under the oak that was in Ophrah, which belonged to Joash the Abiezrite as his son Gideon was beating out wheat in the wine press in order to save it from the Midianites."
Proverbs 8:22 "“The Lord possessed me at the beginning of His way, Before His works of old. “From everlasting I was established, From the beginning, from the earliest times of the earth. “When there were no depths I was brought forth, When there were no springs abounding with water. Before the mountains were settled, Before the hills I was brought forth; While He had not yet made the earth and the fields, Nor the first dust of the world. “When He established the heavens, I was there, When He inscribed a circle on the face of the deep, When He made firm the skies above, When the springs of the deep became fixed, When He set for the sea its boundary. So that the water would not transgress His command, When He marked out the foundations of the earth; Then I was beside Him, as a master workman; And I was daily His delight, Rejoicing always before Him, Rejoicing in the world, His earth,And having my delight in the sons of men." (A description of the eternal Jesus)
Isaiah 48:16 “Come near to Me, listen to this: From the first I have not spoken in secret, From the time it took place, I was there. And now the Lord God has sent Me, and His Spirit.” (A clear picture of the Trinity)
Isaiah 63:10 "But they rebelled And grieved His Holy Spirit; Therefore He turned Himself to become their enemy" (The Holy Spirit as God)
Isaiah 61:1 "The Spirit of the Lord God is upon me, Because the Lord has anointed me"
NT
Matt. 3:16-17 "After being baptized, Jesus came up immediately from the water; and behold, the heavens were opened, and he saw the Spirit of God descending as a dove and [j]lighting on Him, 17 and behold, a voice out of the heavens said, “This is My beloved Son, in whom I am well-pleased.” (A picture of the Trinity, Father, Son, and Holy Spirit)
Matt. 28:19 "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit," (The Great commission, which tells us in whose name we go forth)
1 Cor. 12:4-6 "Now there are varieties of gifts, but the same Spirit. And there are varieties of ministries, and the same Lord. There are varieties of effects, but the same God who works all things in all persons." (God and the Holy Spirit)
2 Cor. 13:14 "The grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit, be with you all." (Self explanatory)
1 Pet. 1:1-2 "To those who reside as aliens, scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia, who are chosen according to the foreknowledge of God the Father, by the sanctifying work of the Spirit, to obey Jesus Christ and be sprinkled with His blood: May grace and peace be yours in the fullest measure."
Jude 20:21 "So Jesus said to them again, “Peace be with you; as the Father has sent Me, I also send you."
John 1:1 "In the beginning was the Word, and the Word was with God, and the Word was God."
John 14:26 "But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all that I said to you."
Romans 8:27 "In the same way the Spirit also helps our weakness; for we do not know how to pray as we should, but the Spirit Himself intercedes for us with groanings too deep for words; and He who searches the hearts knows what the mind of the Spirit is, because He intercedes for the saints according to the will of God.
And before someone asks why Jesus appears to be talking to himself at times, it's because he is a distinct person from the Father. Athanasius tells us that the Son is not the Father but equal to the Father, The Holy Spirit is not the Son, but is equal to the Son, the Father is not the Holy Spirit, but is equal to the Holy Spirit, for all are God, yet distinct from one another. Jehovah's Witnesses will say "We don't hold to the words of Athanasius, he is a mere man". Yet their creator, Charlie Russel, was a mere man, and will lead them into the hell they don't believe exists.