Consider the following Bible passages.
To you it was shown, that you might know that YHWH is God and there is no other besides Him. (Deuteronomy 4:35).
Do you thus repay YHWH, O foolish and unwise people? Is not He your Father who has bought you?... See now that I, I am He, And there is no god besides ME (Deuteronomy 32:6-39).
Yet, the LORD, the God of Israel, chose me from all the house of my father to be king over Israel forever. For He has chosen Judah to be a leader; and in the house of Judah, my father's house, and among the sons of my father He took pleasure in me to make me king over all Israel.... He said to me, `Your son Solomon is the one who shall build My house and My courts; for I have chosen him to be a son to Me, and I will be a father to him... As for you, my son Solomon, know the God of your father, and serve Him with a whole heart and a willing mind.(1 Chronicles 28:4,6,9).
Have we not all One Father? Has not One God created us? (Malachi 2:10).
Hear, O Israel: YHWH our God, YHWH is One. (Deuteronomy 6:4).
You YHWH, are our Father; we are the clay, and You are our potter; we are all the work of Your hand. (Isaiah 64:8).
There is one God, the Father out of whom are all things and we to Him and one Lord Jesus Christ through who are all things and we to him.
(1 Corinthians 8:6).
I, then, a prisoner for the Lord, urge you to live in a manner worthy of the call you have received,
with all humility and gentleness, with patience, bearing with one another through love, striving to preserve the unity of the spirit through the bond of peace, one body and one Spirit, as you were also called to the one hope of your call, one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all.
There is one God, and one mediator between God and men, the man Christ Jesus. (1 Timothy 2:5).
Father... this is eternal life, that they may know You the only true God... and Jesus Christ whom You sent. (John 17:3).
For they themselves report concerning us what a welcome we had among you, and how you turned to God from idols, to serve a Living and True God, and to wait for His Son from heaven, whom He raised from the dead, Jesus who delivers us from the wrath to come. (1 Thessalonians 1:9-10).
And we know that the Son of God has come and has given us understanding so that we might know Him who is true and we are in Him who is true, in His Son Jesus Christ. This one is the true God and eternal life. (1 John 5:20).
I have come in the name of my Father and you do not receive me but if another comes in his own name you will receive him. How can you believe receiving glory from one another and do not seek the glory that comes from the only God? (John 5:43-44).
Believe in God; believe also into me. In my the house of my Father are many rooms. If it were not so, would I have told you that I go to prepare a place for you? And when I go and prepare a place for you, I will come again and will take you to myself, that where I am you may be also. And you know the way where I am going." Thomas said to him, "Lord, we do not know where you are going; how can we know the way?" Jesus said to him, "I am the Way, and the Truth, and the Life; no one comes to the Father , but by me. (John 14:1).
My God, My God, why have you forsaken me. (Matthew 27:46).
I am ascending to my Father and your Father, to my God and your God. (John 20:17).
You have loved righteousness and hated lawlessness; Therefore God, your God, has anointed you with the oil of gladness above than your comrades [the angels]." (Hebrews 1:9).
[Jesus] has made us kings and priests to his God and Father." (Revelation 1:6).
He who conquers, I will make him a pillar in the temple of my God. Never shall he go out of it, and I will write on him the name of my God, and the name of the city of my God, the new Jerusalem which comes down from my God out of heaven, and my own new name. (Rev 3:12).
The Head of Christ is God. (1 Corinthians 11:3).
I charge you in the sight of God... who gives life to all, and of Christ Jesus, who testified the good confession before Pontius Pilate, that you keep the commandment spotless and irreproachable until the appearing of our Lord Jesus Christ, which in his own time he will show, the Blessed and only Sovereign Power (dynastes), the King of Kings and Lord of Lords, who alone possesses immortality and dwells in unapproachable light, whom no man has ever seen or can see. To Him... be honor and eternal might! Amen. (1 Timothy 6:14-16).
What qualities are necessary to be "God?" Can a being be inferior in any respect to God and be God? Is it enough to have many things in common with God to be God? Can one be God by identity if one shares things in common with God? Or, is it true that God by definition can have no one above him or greater than him in any positive respect? If one is positionally inferior to God then can one be God? Can God have a God?
The Scriptures reveal plainly that the Father enjoys several distinctions his Son does not share and can never share. Most Trinitarians do not even realize some of these things and wish to overlook those things they do realize. The Father is positionally above the son by virtue of his Fathership. The Son is below the Father due to his Sonship. The Son has a Father over him but the Father does not. The Son has a Father but the Father does not have any Father. The Father is unbegotten but the Son is begotten. It matters not how anyone defines "begotten"; it will still remain that the Son is begotten and the Father is not. The Son is sourced in the heart of the Father but the Father is sourced in no one. The Father is the creator of all things. The Son is never said to have created but was the means by which the Father created, His Word. The Father omnisciently knows all things and the Son does not. There is no evidence whatsoever that the Son only temporarily did not know the day or hour. Indeed, neven after the resurrection Jesus says the Father fixes times and seasons by his own authority. The Father is immutable, unsusceptible to change. The Son changed in his incarnation and became subject to death, a death from which only the Father could save him. And the Bible does explicitly say that Jesus called out to the One who could save him. God is life by definition and the Son of God was mutably dead. The Son changed again in his resurrection when he was glorified with his Father's glory and power. The Father lives by the omnipotence of his own immortal life. The Son does not live by the power of his own immortal life but lives by the omnipotent power of his Father's immortal life. The Son had, and has, a Lord above him, but the Father has no Lord above Him. The Son had, and has, a God above him, but the Father has no God above Him. The Son of God will always be subject to his Father. The Father never has been, nor ever will be, subject to anyone. God has no God, but the Son of God does have a God. The Father is greater than all, including His Son. He is God Most High, YAHWEH, the Father of Jesus Christ, the God which Jesus of Nazareth worshiped and served and worships and serves. The Scriptures explicitly and plainly teach all these things.
These are some of the reasons we can be sure that only the Father is God. To be God you cannot be inferior to any other being in any respect, not one. Jesus is inferior to God the Father in many respects. God is spirit. Truly, the risen Jesus shares the same divine nature of glory as his Father. He is qualitatively equal with his Father by nature. But he does not share his Father's position and that is why he is not "God" by identity. Jesus is quantitatively inferior to God his Father. Jesus is quantitatively, and qualitatively, superior to every single being but one, God. Jesus has always been subject to God as a word is always subject to its own source and Master. He is the Word of God.