Anyone who knows what it is about the Lord that “the Son of God” means and what it is about him that “the Son of Humanity” means can see many hidden wonders in the Word, since the Lord calls himself sometimes the Son, sometimes the Son of God, and sometimes the Son of Humanity, in each case depending on the subject of the discourse.
When the subject is his divinity, or his being one with the Father, or his divine power, or faith in him, or life from him, then he calls himself “the Son” and “the Son of God,” as in John 5:16–26 and elsewhere. When the subject is his suffering, though, or his judging, or his Coming, or more generally his redeeming, saving, reforming, or regenerating us, then he calls himself the Son of Humanity. This is because it then means himself as the Word.
The Lord is identified by various names in the Word of the Old Testament. There he is called Jehovah, Jah, the Lord, God, the Lord Jehovih, Jehovah Sabaoth, the God of Israel, the Holy One of Israel, the Mighty One of Jacob, Shaddai, the Rock, as well as Creator, Maker, Savior, Redeemer—always depending on the subject of the discourse. This is the case in the Word of the New Testament, too, where he is called Jesus, the Christ, the Lord, God, the Son of God, the Son of Humanity, the Prophet, and the Lamb, among other names, again always depending on the subject of the discourse.
So far we have been talking about why the Lord is called the Son of God. Now we must turn to why he is called the Son of Humanity.
He is called the Son of Humanity when the subject is his suffering, his judging, his Coming, or more generally his redeeming, saving, reforming, or regenerating us. This is because the Son of Humanity is the Lord as the Word; and it is as the Word that he suffered, judges, comes into the world, redeems, saves, reforms, and regenerates. What follows may serve to demonstrate that this is the case.
The Lord is called the Son of Humanity when the subject is his suffering. This we can tell from the following passages.
Jesus said to his disciples, “Behold, we are going up to Jerusalem, and the Son of Humanity will be betrayed to the chief priests and to the scribes; and they will condemn him to death and hand him over to the Gentiles, and they will whip him, and spit on him, and kill him. On the third day, though, he will rise again.” (Mark 10:33, 34)
Likewise elsewhere, where it foretells his suffering, as in Matthew 20:18, 19; Mark 8:31; Luke 9:22:
Jesus said to his disciples, “Behold, the hour is at hand, and the Son of Humanity is being betrayed into the hands of sinners.” (Matthew 26:45)
The angel said to the women who came to the tomb, “Remember what he said to you: ‘The Son of Humanity must be betrayed into the hands of sinful people and be crucified and rise again on the third day.’” (Luke 24:6, 7)
The reason the Lord then called himself the Son of Humanity is that he allowed people to treat him the way they were treating the Word, as has already been explained more than once [Sections 14–16].
from The Lord, Sections 22-24
Sections 14: Published 3/2/2018
Sections 15-16: Published 3/7/2018-3/11/2018