John 8:16-18, “You judge after the flesh; I judge no man. And yet if I judge, my judgment is true: for I am not alone, but I and the Father that sent me. It is also written in your law, that the testimony of two men is true. I am one that bears witness of myself (God as man), and the Father that sent me bears witness (God as God) of me.”
John 5:26 (ESV), “For as the Father has life in himself (God as God), so he has granted the Son also to have life in himself (God with us as a man).”
While the Father has always been the timeless divine Holy Spirit without a beginning in time, the Son of God was “granted life in himself” as a distinct human life with a specific beginning in time. For John 5:26 states that the Son was “GRANTED (didómi means “to give”) LIFE (zoe means “life”) in himself by being “MADE (homoioó: “to make”)... fully human in every way” (Heb. 2:17) as a true human being. This explains why Psalm 2:7 says, “You are My son this day have I given BIRTH to you (“yalad” is the same word used for the births of Cain and Abel in Gen. 4:1-2)”. And this is why God the Father said during the Old Testament time period, “I will be to him a Father and he will be to me a Son” in the prophetic future (Hebrews 1:5 cites 2 Samuel 7:14).
Just as the omnipresent Father outside of the incarnation has a “life in Himself (John 5:26),” so the living Father has “granted the Son also to have life in himself” within the incarnation via virgin conception and birth. Thus we have only “One God” (who is the omnipresent Father) and one mediator between God and men, “the man Christ Jesus” (1 Tim. 2:5) as the Son who was granted a distinct human life within the virgin. This explains how the distinct human life of the Son of God within the incarnation could give testimony as one distinct human witness, while the Father as the Father remained unchangeable in the heavens to give testimony as one distinct divine witness. This is precisely what we would expect if we are to believe that God became a man via virgin conception and birth.
When the omnipresent God became a man within the virgin, He entered into a distinct human life inside of the incarnation. This explains how Jesus could experience human attributes inside of the incarnation as a distinct human son while He simultaneously remained distinct with His divine attributes outside of the incarnation as the omnipresent Father. For God as God always remained unchangeable in the heavens (Malachi 3:6, “I am Yahweh, I change not”) while God also simultaneously became a man (Heb. 1:3 “who being the brightness of His glory and the express image of His Person” – the Father’s Person; Heb. 2:14-17; Heb. 13:8) in order to “save His people from their sins” (Matthew 1:18-23). Therefore, Jesus as a child born and Son given was “made … fully human in every way” (Heb. 2:17 NIV) while He has always existed without a beginning as “the Mighty God” and “Everlasting Father” (Isaiah 9:6; John 14:7-9) who remains “the same yesterday, today, and forever” (Heb. 13:8) in his divinity.
Since Numbers 23:19 proves that “God is not a man,” we know that Jesus is not literally God with us as God, but rather, Immanuel “God with us” as a true man who had the capacity to pray, suffer, and be tempted. James 1:13 (ISV) says that “God cannot be tempted by evil, nor does he tempt anyone.” Hence, we know that Jesus is not God with us as God, but God with us as a distinct man who lived an authentic human life. Therefore, only the omnipresent God who is our Heavenly Father is the only Being who can simultaneously become a man with a distinct human life (as the Son) in order to save us while remaining unchangeable in the heavens with His distinct divine life (as the Father). This explains how only God Himself can remain One in His Essence of Being with a distinct divine testimony within Himself while also becoming a distinct human son with a distinct human testimony within himself.