When he used the epithet son of God he was referring to that part of him which was related to God, i.e. his soul or spirit.
We are all products of both the world and God.
We all have personalities which have been formed by reaction to the world around us and experiences in the world.
We all also have aspects of ourselves which are formed, directly or indirectly, by God.
It was O.K. for Jesus to call himself son of man because that meant to the Pharisees that he was born in sin and in need of redemption through them.
It was not O.K. for Jesus to call himself son of God because that meant that he had some sort of relationship with God which was outside of the Pharisees' control.
"'And call no one your father on earth, for you have one Father - the one in heaven.'" Matthew 23:9 (NRSV)
We don't need the Pharisees to have a relationship with God.
That is not to say that God is not in His house. He is. That is why Jesus went to Jerusalem - to go to God's house. When he got there, however, he behaved unpredictably. He criticized the authorities. He said that they had perverted God's message - turning love and compassion into privilege and profit.
They crucified him for that.
Why did God not stop them?
Perhaps God could not stop them.
They would not listen to Him speaking through His prophet.
God does not use force.
"'For I tell you, you will not see me again until you say, "Blessed is he who comes in the name of the Lord."'" Matthew 23:39 (NRSV)
"'Wherever the corpse is, there the vultures will gather.'" Matthew 24:28 (NRSV)
The Pharisees had usurped the power of God (the temple) for their own profit.
And they did not share power.
It is the same today in Jesus' Church = money and power.
So we are all sons of man and sons of God despite what the Churches may tell you.
Our task is to return the message of love and compassion to its rightful place in God's house.
Until then the blind lead the blind.
(Scripture quotations (marked NRSV) are taken from the New Revised Standard Version Bible, copyright 1989 by the Division Of Christian Education of the National Council of the Churches of Christ in the U.S.A., and are used by permission. All rights reserved.)