The term, ‘son of man’ is used 193 times in the Bible.  Throughout the Old Testament we find this term describing men.  The first time we see this is in Numbers 23:19, “God is not a man, that he should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good?”  ‘Son of man’ simply means a person is ‘the product of a man, or mankind.’  In that sense, we are all sons, or children, of men, or mankind.

The first time in the New Testament that we see this term is when the Lord Jesus applies it to Himself in Matthew 8:20, “And Jesus saith unto him, The foxes have holes, and the birds of the air have nests; but the Son of man hath not where to lay his head.”  Applying this term to Himself, the Lord is acting in meekness and humility, declaring that He too, is a product of mankind.  What a blessed and encouraging thing it is that the Lord would identify Himself with us like that.  We even have two genealogies of the Lord Jesus.  Matthew 1 shows His heritage through His mother, Mary.  Luke 3 shows His heritage through his supposed father, Joseph.  The Lord Jesus refers to Himself as ‘son of man’ over 75 times, but it is interesting to note that no one else refers to Him as ‘son of man’ EXCEPT Stephen as he is being martyred in Acts 7:56.  There with all the stones being thrown at him, Stephen declares, “Behold, I see the heavens opened, and the Son of man standing on the right hand of God.”  This shows us that even after the death, resurrection, and ascension of our Lord, He is still the SON OF MAN.

The first time we read the term ‘Son of God’ is in Daniel 3:25, “He answered and said, Lo, I see four men loose, walking in the midst of the fire, and they have no hurt; and the form of the fourth is like the Son of God.”  Of course this is in reference to the time when Shadrach, Meshach, Abednego were cast into the fiery furnace because they refused to bow to an idol.  The Son of God here is most likely a Theophany, or a pre-incarnate appearance of the Lord Jesus.

While no one referred to the Lord Jesus as ‘son of man’, we have several people refer to Him as Son of God.  Demons called Him Son of God in Matthew 8:29, “And, behold, they cried out, saying, What have we to do with thee, Jesus, thou SON OF GOD? art thou come hither to torment us before the time?”  His disciples called Him Son of God in Matthew 14:33, “Then they that were in the ship came and worshipped him, saying, Of a truth thou art the SON OF GOD.”  John the Baptist said of the Lord Jesus in John 1:34, “And I saw, and bare record that this is the SON OF GOD.”  Martha, the sister of Lazarus said in John 11:27, “Yea, Lord: I believe that thou art the Christ, the SON OF GOD, which should come into the world.”  The Roman centurion who pierced the Lord with a sword while on the cross called Him the Son of God in Matthew 27:54, “Now when the centurion, and they that were with him, watching Jesus, saw the earthquake, and those things that were done, they feared greatly, saying, Truly this was the SON OF GOD.”  We could continue with more examples of others calling the Lord Jesus the Son of God, but that is enough.  Of course, the Lord Jesus referred to Himself as the Son of God several times.  For example, we read the words of Jesus in John 10:36, “Say ye of him, whom the Father hath sanctified, and sent into the world, Thou blasphemest; because I said, I am the Son of God?”

The simple answer to your question, “Why is Jesus referred to as both the Son of Man and the Son of God?” is that the Lord Jesus referred to Himself as both son of man and Son of God.  It is so precious to realize that the Son of God became the son of man so that the sons of men might become the sons of God.  John 1:12 says, “But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name.”  Dear friend, are you a son (child) of God?  Have you received the Lord Jesus Christ as your savior?  Please, do not delay in putting your faith in the Lord Jesus Christ.  Tomorrow may be too late!  (202.10)