Let us look how Paul used the term "son of..." when speaking to a sorcerer named Elymas:
"O full of all deceit and all fraud, you son of the devil, you enemy of all righteousness, will you not cease perverting the straight ways of the Lord?" (Acts 13:10).
Of course Paul was not saying that Elymas was a literal son of the devil. Instead, he was saying that the "nature" of Elymas is that of the devil. So when it is said that the Lord Jesus is the "son of man" what is being said that His nature is that of man. And when it is said that He is the "son of God" what is being said is that His very nature is that of God.
Let us look at the way that
the Unitarians understood the term "son of man" in regard to the Lord Jesus. The say:
"He did not 'toot his own horn,' but instead called himself 'the son of man,' which, in the Aramaic language he spoke, meant 'a man'" (biblicalunitarian.com).
Since in the Aramaic language the term "son of man" means "man" then we can understand that in the same language the term "son of God" means "God."
The same can be said about the way the Lord Jesus used the word "Father" when speaking to unbelievers:
"Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it" (Jn.8:44).
The Lord Jesus was not saying that their real father was actually the devil. Instead, he was saying that their "nature" is that of the devil.
When the Lord Jesus told the Jews that God was His Father they knew that He was claiming to be God:
"But Jesus answered them, My Father worketh hitherto, and I work. Therefore the Jews sought the more to kill him, because he not only had broken the sabbath, but said also that God was his Father, making himself equal with God" (Jn.5:17-18).
If this was just a misunderstanding and the Lord Jesus is not equal to God then there can be no doubt that He would have cleared up this misunderstanding and said that He was not claiming to be God. However, what He told them only made it plainer that He was claiming to be God.
First, He told them that He had the same power to raise up the dead as does the Father (v.21). He then said that all judgment has been committed to Him (v.22). Then He told them this:
"That all men should honour the Son, even as they honour the Father. He that honoureth not the Son honoureth not the Father which hath sent him" (Jn.5:23).
There can be absolutely no doubt that by those words the Lord Jesus was confirming the Jews' idea that He was making Himself equal to God. And there is no reason at all why He would say those things unless He is God.