If Yeshua is the Son of God,
why is he also referred to as the "Son of Man"?

Philippians 2:5 And think you so in yourselves, as Y'shua the Mashiyach also thought; 6. who, as he was in the likeness of Elohim, did not regard it sinful to be the coequal of Elohim; 7. yet disinherited himself and assumed the likeness of a servant, and was in the likeness of men and was found in fashion as a man; 8. and he humbled himself and became obedient to death, even the death of the stake. 9. Wherefore, also, Elohim has highly exalted him and given him a name which is more excellent than all names; 10. that at the name of Y'shua every knee should bow, of (beings) in heaven and on earth and under the earth; 11. and very tongue will avow MarYah - that is, Yeshua the Messiah - to the glory of His Father. (AENT) . (AENT)

Yeshua was an arm of YHWH (Isaiah 53:1). He was not the "Father", but he was divine because he came directly from the Father:

II Samuel 7:14 - I will be a father for him, and he will be a son for me. IF he does something wrong, I will punish him with a rod and blows, just as everyone gets punished;

Psalm 2:7 - "I will proclaim the decree" Adonai said to me, 'You are my son; today I became your father...

YHWH was not referred to as the "Father" before Yeshua's birth. The Father's existence was not even fully understood until after the Messiah came:

Matthew 11:27 - "My Father has handed over everything to me. Indeed, no one fully knows the Son except the Father, and no one fully knows the Father except the Son and those to whom the Son wishes to reveal him.

Luke 10:22 - "My Father has handed over everything to me. Indeed, no one fully knows who the Son is except the Father, and who the Father is except the Son and those to whom the Son wishes to reveal him.

It was not until Messiah's birth to a human mother, that he was given the title "Son of Man." We must realize it was necessary for Yeshua to come as a human (albeit, a human with a divine qnoma/nature, because he was not born of human sperm, but by supernatural methods from YHWH, his "Father") - and there were several reasons for this:

GOD Himself cannot be born or die; and so He sent a human Messiah - whose ultimate goal was to preach the Kingdom, do everything his Father commanded, and then martyr himself, thus shedding his divine blood to become our redemption. (See Luke 4:43 and 8:1; and Acts 24:14 and 28:23.) Being a suffering human helped Yeshua (and consequently, YHWH Himself)...

Hebrews 4:15 - For we do not have a cohen gadol (high priest) unable to empathize with our weaknesses; since in every respect he was tempted just as we are, the only difference being that he did not sin.

This entire scenario was part of YHWH's Master Plan of salvation for mankind. Among the many titles by which Yeshua was known in the Old Covenant, "Son of Man" reveals one of Messiah's many important characteristics.

Daniel 7: 9 I beheld till thrones were placed, and one that was ancient of days did sit: his raiment was as white snow, and the hair of his head like pure wool; his throne was fiery flames, and the wheels thereof burning fire. 10 A fiery stream issued and came forth from before him; thousand thousands ministered unto him, and ten thousand times ten thousand stood before him; the judgment was set, and the books were opened. 11 I beheld at that time because of the voice of the great words which the horn spoke, I beheld even till the beast was slain, and its body destroyed, and it was given to be burned with fire.

12 And as for the rest of the beasts, their dominion was taken away; yet their lives were prolonged for a season and a time. 13 I saw in the night visions, and, behold, there came with the clouds of heaven one like unto a son of man, and he came even to the Ancient of days, and he was brought near before Him. 14 And there was given him dominion, and glory, and a kingdom, that all the peoples, nations, and languages should serve him; his dominion is an everlasting dominion, which shall not pass away, and his kingdom that which shall not be destroyed.

Further explanation from the Aramaic English New Testament:

John 10: 30 "I and the Father are one."

The intimate relationship between Father and Son unfolds in Matthew 6:9-13 with the Prayer of our Master, and progressive revelation continuing in Matthew 26:39, 42 and so on. Put simply, if Yeshua is YHWH, then is he talking to himself? The answer, of course, is NO! But, in order to understand we must go deep into the Tanakh ("Old Testament") to the following milestone passages:

(1) In Exodus 23:20-22 we find mention of the only Messenger that YHWH sent to Israel who "has My Name in him." This is key because every other messenger has YHWH's title - EL (MichaEL, RaphaEL, UriEL, etc.) in their names. But Y'shua's name means, "YHWH is salvation" which is tied to prophecy about him in places like Jeremiah 23:5-6, and fulfilled in John 17:11. Mashiyach has a superior name to the other messengers (Hebrews 1:1-5) and a Name in him that is above all other names (Colossians 1:16-19, Philippians 2:9-10). This means that Y'shua and this Messenger, who are one and the same, have the Name Yah rather than El/Eloah/Elohim.

(2) The other aspect of Exodus 23:20-22 is that YHWH warns that this Messenger will not forgive Israel if they sin; implying that he had the independent power to do so, but would not on this occasion. Such ability was not ever afforded any other heavenly messenger. To see how this might manifest with Mashiyach's power and office, please see Matthew 9:5-8.

(3) Isaiah 9:6 tells us that one of the names of Mashiyach is "the Everlasting Father," who is obviously YHWH Himself. Then Isaiah 11:1-2 tells us that Mashiyach as the Root of Jesse will have the Spirit of YHWH rest inside him! Incidentally, the Spirit of YHWH and the Ruach haKodesh are also one and the same, as evidenced by Psalm 51:1-11 and Isaiah 63:1-11.

(4) Perhaps the most essential passage is in Zechariah 12:10, where the only begotten Son is killed but YHWH is "pierced." The Hebrew here, in spite of rabbinic argumentation to the contrary, could not be clearer. The phrase in question is et asher dakaru. The et serves as a direct object pointer; it shows what part of a Hebrew sentence is receiving the action. So in Genesis 1:1 we are told et hashamayim v'et ha'aretz, with the et meaning that the heavens and the Earth are receiving the action of being created.

On this everyone agrees, but the same rabbis who agree with this usage everywhere else in Tanakh turn a blind eye here. In this passage, it can only read as "to whom pierced they," and since YHWH is speaking, He is being pierced! And yet the rest of the passage talks of people mourning for the man as "an only begotten son"! How can this be? The Son whose flesh is pierced contains an occurrence (qnoma in Aramaic) of YHWH's Spirit, so while it is the flesh that is literally pierced and dies, the Spirit of YHWH is pierced too, but of course, cannot die.

(5) Finally Isaiah 53:1: "to whom has the arm of YHWH been revealed?" This is the only acceptable form of "Godhead" in Scripture. Clearly not a Trinity of three separate beings (or persons), because the arm is not a separate entity from the rest of the body and has no independent will. The "arm" moves only with the power and control from the mind. In the same way YHWH's nature is manifest as an occurrence within the Son that is separate but side-by-side with his human nature. These two natures then communicate with one another; thus explaining why Y'shua is not talking to himself when he prays to his Father.

This fact is also why sometimes Y'shua says things like, "My teaching is not my own" and "I can do nothing without my Father" on the one hand but on the other he says, "If you have seen me, you have seen the Father" and "I and my Father are one of the same." This indicates a 100 percent divine nature that exists in a 100 percent human soul and flesh, where one or the other talks through Y'shua. But the human is subject to the divine (again, "Not my will...") which is the only way the Scripture cannot be broken. It is not Trinity but neither does this deny the divine aspects in Y'shua himself. It is also the real meaning behind, "No one comes to the Father but by me." See also John 5:26.