Jesus called Himself Son of Man to identify Himself with us. This title comes from the Old Testament, the Book of Daniel 7, verse 13:
“In my vision at night I looked, and there before me was one like a son of man coming with the clouds of heaven. He approached the Ancient of Days and was led into his presence."
Even though the Old Testament is mainly written in Hebrew, this passage in Daniel 7 is written in Aramaic. Personally I think it's very probable that Jesus spoke Aramaic so He would actually be using this title Baranush, the Aramaic form for ‘Son of Man’. For the Jewish people for His day, the moment he used that phrase, Baranush, it was virtually, without any question, a claim to be the Messiah.
Jesus used this title, Son of Man, of Himself in two different aspects. He applied it to Himself in humility. For instance in Matthew chapter 8, verse 20:
Jesus said, "Foxes have holes and birds of the air have nests, but the Son of Man has no place to lay his head." (NIV)
A kind of wanderer, without a fixed residence or abode. And in Matthew 20, verse 28, Jesus says:
"Just as the Son of Man did not come to be served, but to serve, and to give His life as a ransom for many." (NIV)
But Jesus also applied it to Himself in glory, for the future. He says in Matthew 16, verse 27:
“For the Son of Man is going to come in His Father's glory with His angels, and then he will reward each person according to what he has done.” (NIV)
And in Matthew 26, verse 64:
"In the future you will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven." (NIV)
That's very close to Daniels' vision, which speaks of the Son of Man in His glorified, revealed being as the appointed ruler by God for the whole universe.
So we have this interesting paradox of the Son of Man representing frailty and weakness and yet being the one who the Jewish people looked for to as the one who would restore the kingdom to Israel and become the ruler of all nations. Now that we are united with Christ by faith, we also identify with these two aspects of Him, the Son of Man.
Lord Jesus, please help to understand that, on the one hand, You identify with me in my frailty and weakness, and as such, You’ve come alongside me, but that on the other hand, You are also the King of kings and the Lord of Lords, mighty in power and glory! I worship You, Lord, and I love You!