He was even calling God his own father, making himself equal with God. (NIV)
1. The peoples in the time and culture of the Bible knew that children often carried the authority of the family. For example, the son of a king had authority. When Christ said that God was his Father, the Pharisees correctly interpreted that to mean that he had God’s authority on earth, something that Jesus was in fact saying (cp. John 5:17ff).
2. This verse is actually unsupportive of the Trinity. It accurately records that Jesus was saying that God was his father, not that he was himself God, or that he was “God the Son.” It is clear that Jesus’ authority came from the fact that he was the Son of God, not God Himself.
3. The concept of people being “equal” is found in several places in the Bible. For example, when Joseph was ruling Egypt under Pharaoh, Judah said to him, “You are equal to Pharaoh himself” (Gen. 44:18). Paul wrote about men who wanted to be considered “equal with us” (2 Cor. 11:12). No Christian we are aware of believes that Joseph and Pharaoh or Paul and his opponents are “of one substance,” and make up “one being” simply because they are called “equal.” We believe that John 5:18 should be handled like the other verses that mention equality. Jesus was using God’s power and authority on earth, and was thus “equal” to God in the same way Joseph, who was using Pharaoh’s authority and power, was equal to Pharaoh.
Morgridge, p. 43
Racovian Catechism, p. 133