… and made us a kingdom, priests to his God and Father, to him be glory and dominion forever and ever. Amen (Rev 1:6)
This is just one of a number of passage which speak of the God of Jesus:
And at the ninth hour Jesus cried with a loud voice, “Eloi, Eloi, lema sabachthani?” which means, “My God, my God, why have you forsaken me?” (Mark 15:34; cf. Matt 27:46)
Jesus said to her, “Do not cling to me, for I have not yet ascended to the Father; but go to my brothers and say to them, ‘I am ascending to my Father and your Father, to my God and your God.’” (John 20:17)
that together you may with one voice glorify the God and Father of our Lord Jesus Christ (Rom 15:6)
Blessed be the God and Father of our Lord Jesus Christ, the Father of mercies and God of all comfort (2 Cor 1:3)
Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places (Eph 1:3)
that the God of our Lord Jesus Christ, the Father of glory, may give you the Spirit of wisdom and of revelation in the knowledge of him (Eph 1:7)
Blessed be the God and Father of our Lord Jesus Christ! According to his great mercy, he has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead (1 Pet 1:3)
The clear and consistent message of these passages is that Jesus has a God, who is identified as his Father. And Jesus showed the truth of these clear statements throughout his earthly life in the way he interacted with God in prayer.
This presents two challenges to Trinitarian thinking. Firstly, it entails that God be identified with someone distinct from Jesus (i.e. the Father). Jesus cannot have a God and also be God without positing two gods. Secondly, it entails a hierarchy with Jesus below God.
Now a Trinitarian might suppose that Jesus had pray to the Father as a God, whilst on the earth, because he was subordinated to God by being in the flesh. However that will not answer passages like Rev 1:6 where it is the resurrected and exalted Jesus who is described as having a God. Alternatively a Trinitarian might argue that “God” in these passages is used in a relational rather than substantial sense. But, even if true, this still has Jesus in a unequal relationship with the Father, his God.
Given the difficulty of devising a suitable reconcilation, we should take these words at face value – Jesus recognised someone distinct from himself as his God and that person is the Father, “the only true God” (John 17:3).