Why did people call Jesus as Son of David and Son of Man when he was neither born to any man or to anyone in the Davidic line? Were they fooling or flattering him, or is it true? If it is true can you give concrete answers?
Who is the Son of David? Jesus Christ or the Lord God? (Luke 20:41-42)
Who gets the throne of David? Jesus or the Lord God and how (Luke 1:32)?
In the Bible, "son" doesn't just refer to an immediate descendant. A grandson, great-grandson, etc. can all be called a "son." Jesus was a descendant of David physically through his mother. That lineage is traced in Luke 3:23-31. Jesus' right to the throne of David is traced through Joseph. Luke traces Jesus lineage all the way back to Adam to prove that through his mother, Jesus was physically a son of man.
Joseph was not physically Jesus' father, but because Joseph and Mary were married prior to Jesus' birth, Jesus is counted as Joseph's son. We still use similar laws here in the United States. Joseph's lineage is traced in Matthew 1. Joseph was also of the lineage of King David, but more importantly, Joseph was in line for the throne of David.
Understanding this is important because in the Old Testament, there was a prophecy that none of King Jeconiah descendants would rule (Jeremiah 22:24-30). This created an apparent impossibility. If the kingship is passed father to son, but none of King Jeconiah's descendants would rule, then how could the Messiah, the son of David, rule? The answer is that Jesus inherited the throne through Joseph without being a physical son of Joseph, and at the same time was still a son of David through his mother.
Jesus was unique in history. He was the inheritor of the legal rule of Israel without physically being a descendant of the last king in the lineage of David -- Jeconiah.
Jesus' question in Luke 20:41-44 brings out a difficulty that the leading Jews had concerning the nature of the Messiah. "And He said to them, "How can they say that the Christ is the Son of David? Now David himself said in the Book of Psalms: 'The LORD said to my Lord, "Sit at My right hand, Till I make Your enemies Your footstool."' Therefore David calls Him 'Lord'; how is He then his Son?"" (Luke 20:41-44).
Since the leading Jews refused to believe that Jesus was the Messiah, Jesus asked them whose son was the Christ (Matthew 22:41-42). They answered that he would be the son of David. Mark 12:35 points out that this is as the scribes had been teaching the people. Jesus then asks them how David, in Psalm 110:1, could call the Messiah his Lord when the Messiah was his descendant. The word "Lord" is reserved for a person who is over the person, yet a descendant would normally be seen as under the ancestor. In asking, Jesus rules out a mistake on David’s part by emphasizing that David spoke these words by the inspiration of the Spirit of God.
The answer to Jesus’ question is clear if one accepts that the Messiah was superior to David because of his divine nature. Yet, those Jesus was addressing would not accept that God could be born in human form, thus they could not determine an answer to Jesus’ question. In other words, their expectation concerning the Messiah was less than what the Scriptures indicted.
The question makes it appear that God cannot be a descendant of David. Yet, that is exactly what happened. "Let this mind be in you which was also in Christ Jesus, who, being in the form of God, did not consider it robbery to be equal with God, but made Himself of no reputation, taking the form of a bondservant, and coming in the likeness of men. And being found in appearance as a man, He humbled Himself and became obedient to the point of death, even the death of the cross. Therefore God also has highly exalted Him and given Him the name which is above every name, that at the name of Jesus every knee should bow, of those in heaven, and of those on earth, and of those under the earth, and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father" (Philippians 2:6-11). This is why one of Jesus' name is Immanuel, which means "God with us" (Matthew 1:23).
As Philippians 2:6-11 points out, Jesus received the throne from His Father after his death. Such was prophesied by Daniel: "I was watching in the night visions, And behold, one like the Son of Man, coming with the clouds of heaven! He came to the Ancient of Days, and they brought Him near before Him. Then to Him was given dominion and glory and a kingdom, that all peoples, nations, and languages should serve Him. His dominion is an everlasting dominion, which shall not pass away, and His kingdom the one which shall not be destroyed" (Daniel 7:13-14). Gabriel told Mary the same thing: "He will be great, and will be called the Son of the Highest; and the Lord God will give Him the throne of His father David" (Luke 1:32).
"In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through Him, and without Him nothing was made that was made. ... And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth" (John 1:1-3, 14).