“As soon as Jesus was baptized, He went up out of the water. Suddenly the heavens were opened, and he saw the Spirit of God descending like a dove and resting on Him. And a voice from heaven said, “This is My beloved Son, in whom I am well pleased!” Matthew 3:16-17 BSB
"Behold, My Servant, whom I uphold; My chosen one in whom My Soul delights. I have put My Spirit upon Him; He will bring forth justice to the nations.” Isaiah 42:1 NASB
According to Isaiah, God the Father put His own Spirit upon the Messiah (“I have put My Spirit upon him” – Isaiah 42:1). Here we see that our only true God the Father spoke from heaven while His own omnipresent Spirit descended like a dove upon the man Christ Jesus. Thus we only see One Divine Person who is our Heavenly Father speaking and descending from heaven upon one human person. For God’s Divine Person (“My Soul” = One Divine Person in Isaiah 42:1) also became one human person via incarnation through the virgin (Heb. 1:3 states that Jesus “…is the brightness of His glory and the express image of His Person,” i.e. The Father’s Divine Person became a human person).
Nothing in this text shows three coequal God Persons at Christ’s baptism as we see only “One God and one mediator between God and men, the man Christ Jesus (1 Tim. 2:5).” For the One Divine Omnipresent Spirit Person called the Father “is a Spirit” (Jer. 23:24; John 4:23-24 – “But the hour comes, and now is, when the true worshippers shall worship the Father in Spirit and in truth: for the Father seeks such to worship him. God is a Spirit: and they that worship him must worship him in spirit and in truth”) who remained unchangeable in the heavens (Mal. 3:6 – “I am Yahweh, I change not”; Heb. 13:8) while He also descended upon the man Christ Jesus at his baptism. This was that Holy Spirit of the Father who led Jesus into the wilderness (Matthew 4:1 – “Then Jesus was led up by the Spirit into the wilderness to be tempted by the devil”) and did the might works through him (John 14:10 – “the Father abiding in me, He does the works”). For when God became a man via incarnation through the virgin, that man was “granted” a distinct human “life in himself” just as “the Father has (a distinct divine) life in Himself” (John 5:26) because God the Father also became a true man person as the Son within the virgin (Matthew 1:20; Hebrews 1:5; Hebrews 2:17). Therefore, the Oneness interpretation has to be the only correct exegesis because God as God “cannot be tempted of evil” (James 1:13), neither can God as God pray to God with a distinct human nature (Numbers 23:19 – “God is not a man”).
Most Trinitarian scholars allege that a Heavenly God the Son Person was both in heaven and on earth at the same time (John 3:13) because a true Yahweh God Person can never vacate His omnipresence in heaven and thus temporarily lose His divine attributes to become a man (Mal. 3:6; Heb. 13:8). For if an alleged coequal Yahweh God the Son Person left heaven to become a man, then inspired scripture which proves that Yahweh God changes not (Mal. 3:6 – “I am Yahweh, I change not”) would be a lie (Heb. 13:8 - “Jesus Christ” as to his divinity remains “the same yesterday, today, and forever”). Wherefore, according to Trinitarian theology, just as an alleged omnipresent heavenly God the Son Person would be able to speak and act in heaven while simultaneously existing on the earth as a man, so according to Oneness theology, our heavenly Father could speak and act in heaven and on earth simultaneously while being incarnated as a human person at the same time.
Since most Trinitarian theologians can think of an alleged omnipresent Son speaking and acting in heaven while He was also on the earth as a man, then it is not unreasonable to believe that the Father could speak in heaven while speaking and acting independently on the earth as a man via His human incarnation in Christ (John 14:7-10, 24). While Oneness theologians admit that it is an impossibility for created angels and men to simultaneously act and speak in more than one geographical location at once, we also acknowledge that our omnipresent Heavenly Father alone has the ability to become a man as His own arm revealed (Isaiah 52:10 – “The LORD [Yahweh] has bared His holy arm In the sight of all the nations, That all the ends of the earth may see The salvation of our God”; 53:1“Who has believed our report and to whom has the arm of Yahweh been revealed”) while retaining His immutable divine attributes in the heavens.
Oneness believers affirm that it is impossible for men and angels to become their own human son. However, we also acknowledge that nothing is impossible for the Almighty who alone is Omnipresent (filling the heavens and the earth at the same time – Jer. 23:24) and who alone has the ability to simultaneously exist, act, and speak in many places at one time as we see at Christ’s baptism. Therefore it is human unbelief that leads to Trinitarian thinking when Trinitarians deny the plain teaching of inspired scripture by saying that our Heavenly Father cannot become incarnate as a child born and son given (Isaiah 9:6 calls the child born and son given, “the Mighty God” and “the Everlasting Father”; John 14:7-9 - “He that has seen me has seen the Father”), and that our Heavenly Father cannot exist as the Holy Spirit (the Father’s Spirit in action – Gen. 1:2 – “the Spirit of God was moving over the surface of the waters”; Luke 1:35 – “the Holy Spirit shall come upon you”; Matthew 3:16-17 – the Spirit of God descending like a dove and resting on Him”) who descended upon Christ at his baptism.