Chizuk Emunah (Pt 2) Under the Microscope: Chapter 58

John 20:17, "Jesus saith unto her [Mary Magdalene], Touch me not; for I am not yet ascended to my Father; but go to my brethren, and say unto them, I ascend unto my Father and your Father, and to my God and your God." Jesus showed here clearly that he was no God, but was in the same subjection to God as his brethren. It cannot, therefore, be asserted on the authority of this passage, that Jesus meant anything more by styling himself "the Son of God," than the Holy Scriptures indicate by such passages as Deuteronomy 14:1, "Ye are children of the Lord your God." The expression "Son of God" has not the slightest reference to a Superhuman Being. 

 Again, what do we expect Jesus to say? You, Father, are just one of many Gods? Troki continues to read the book of John without taking verses 1-18 into context. So let's get to the more important part: Jesus as Son of God. What, exactly, did that mean in the time of Jesus?

The term has many uses. It is often used of kings. Psalm 2 declares the reigning king to be God's son.
I will tell of the decree: The LORD said to me, “You are my Son; today I have begotten you. Ask of me, and I will make the nations your heritage, and the ends of the earth your possession. You shall break them with a rod of iron and dash them in pieces like a potter's vessel.” (Psalm 2:7-9) 

Daniel mentions the Son of God in the furnace episode:

Then King Nebuchadnezzar was astonished and rose up in haste. He declared to his counselors, “Did we not cast three men bound into the fire?” They answered and said to the king, “True, O king.” He answered and said, “But I see four men unbound, walking in the midst of the fire, and they are not hurt; and the appearance of the fourth is like a son of the gods.” (Daniel 3:24-25 ESV)

This reference did have superhuman implications. The term "son of" implied that someone was in that category. The Tanakh had sons of valor (valorous people), sons of wise ones (wise people), sons of rebellion (rebellious people), sons of murder (murderous people), sons of foolishness (foolish people), sons of smiting (those who deserved to be beaten), and sons of tumult (those who were in tumult). S. Herbert Bess goes through more detail in his esssay.

Son of God can mean king of Israel. It was also used of Roman emperors have been decared as "Son of God" in their emperor cults, which was a title of divinity.

Again, I punt to Williams:

Lastly, may one word be added with regard to the teaching of the passage as a whole? Mary Magdalene, when she recognized Jesus after this His resurrection from the dead, fell at His feet saying, "Rabboni!" and, as it appears, was clinging to them. But Jesus saith to her: "Do not stay clinging to Me thus; there is more for thee than this. I am ascending to the Father; then thou shalt have perfect communion and fellowship." Even at that moment of blissful thankfulness at His resurrection, Jesus would draw her thoughts away from the earthly and visible to the unseen, with its promise of intercourse closer than she then enjoyed. The ascended Christ is nearer to believers than He could ever have been on earth. If Christ were reigning as king in Palestine, He would not be as nigh to His servants as He is now, when He is seated in glory.

Son of God is not a prooftext that Jesus was God. The idiom had multiple uses. The phrasing we see in this chapter of John is precisely what the author would convey if he wanted to affirm monotheism (there is one God) and deny unitarianism (God is one person).