The Bible says in many verses that there is only one God and “God” does not have a God. We read in Isaiah 44:6 “…there is no God besides me” and Ephesians 4:6 says there is “one God and Father of all, who is over all.” Jesus has a God in contrast to “God” who alone is God and does not have a God. Jesus spoke about his God after the resurrection to Mary Magdalene, saying “…I ascend to my Father and your Father, and my God and your God” (John 20:17). Jesus still called God “my God” after his ascension into heaven when he was standing at the right hand of God.
There are also verses in the New Testament that clearly speak of “God” being the “God” of Jesus Christ. Romans 15:6 says “...you can, with one mouth, glorify the God and Father of our Lord Jesus Christ.” 2 Corinthians 1:3, Ephesians 1:3, and 1 Peter 1:3 all say “Blessed be the God and Father of our Lord Jesus Christ.” So the “one God and Father” (Ephesians 4:6) is the God of Jesus Christ. The “one God” of the Bible never says He has a God because He is God, the Father, the Creator, “the Most High God” and He has no equals. Jesus is not “God” because he's a man, the last Adam, the created Son of God, and the God of Jesus is God the Father.
In John 5:44 Jesus called the Father “the only God” and The New American Standard Bible goes so far as to translate it as “the one and only God.” The straightforward reading of this verse is that Jesus did not think of himself as God. Jesus prayed to God on the night he was arrested that people would “know you, the only true God” (John 17:3). It seems disingenuous or at least confusing that Jesus would refer to his Father as “the only true God” if he knew that both he and “the Holy Spirit” were also “Persons” in a triune God and that the Father shared His position as “God” with them. It seems much more likely that Jesus spoke the simple truth when he called his Father “the only true God."
Colossians 1:15 calls Jesus “the firstborn of all creation.” Scholars disagree on what this phrase means, but that is primarily because the doctrine of the Trinity obscures its simple meaning. Trinitarian doctrine states that Jesus is “eternal” but if that is true then he cannot be the firstborn “of all creation” because that would make him part of the creation. But the simple reading of Colossians 1:15 seems clear: Jesus is a created being. The BDAG Greek-English lexicon [entry under “creation”] explains the Greek word translated “creation” as “that which is created… of individual things or beings created, creature.” Not only was Jesus a created being, but he's also called the “firstborn” from the dead because he was the first one in God’s creation who was raised from the dead to everlasting life—a point that is also made in Colossians 1:18.