Jesus is a direct descendent of King David
About 1000 years BC, which is about 1000 years after Abraham's days, God took a shepherd boy called David and raised him up to be King of Israel. God also promised that one of King David's descendants would sit on David's throne forever as King of Israel. Jesus, who is the Messiah, is the heir of King David. Therefore He is legally entitled to rule over the nation of Israel as its King. In the future He will do exactly that.
Jesus descends physically from King David and derives His right to sit on the throne of King David through his mother, Mary. Her lineage is shown in the gospel of Luke at Chapter 3. He also descended from King David through his adoptive father, Joseph. This is shown in the gospel of Matthew at Chapter 1. However, He inherited His right to the throne through His mother, Mary, not His step-father, Joseph. Through the prophet Nathan, God had promised King David that one day he would have an heir who would rule on the throne of Israel forever:
12 When your days are over and you rest with your ancestors, I will raise up your offspring to succeed you, your own flesh and blood, and I will establish his kingdom. 13 He is the one who will build a house for my Name, and I will establish the throne of his kingdom forever. 2 Samuel 7:12-13 (NIV)
Your house and your kingdom will endure forever before me; your throne will be established forever 2 Samuel 7:16 (NIV)
God also made a covenant (a binding agreement) with King David that God would establish David's Kingdom for ever and give David an heir (Jesus Christ) who would rule forever:
3"I have made a covenant with My chosen;
I have sworn to David My servant,
4I will establish your seed forever
And build up your throne to all generations."
Psalm 89:3-4 (NASB)
Two centuries later the prophet Isaiah enlarged the details of that prophecy about the coming King and Messiah:
6For to us a child is born,
to us a son is given,
and the government will be on his shoulders.
And he will be called
Wonderful Counselor, Mighty God,
Everlasting Father, Prince of Peace.
7Of the increase of his government and peace
there will be no end.
He will reign on David's throne
and over his kingdom,
establishing and upholding it
with justice and righteousness
from that time on and forever.
The zeal of the LORD Almighty
will accomplish this. Isaiah 9:6-7 (NIV)
That prophesy has not yet had a complete fulfilment through David’s ordinary human lineage, because David’s line lost the kingship several generations later under a king called Zedekiah. They have never regained it since. Thus, for over two thousand five hundred years since then, there has been no Jewish King of Israel. Note that the Kings in Jesus’ day i.e. King Herod and his sons, were not Jewish. They were Edomites. They were put in place by the Romans and were nothing to do with the royal line of King David.
But there is a day coming when Jesus Christ, the Jewish Messiah, and the rightful King of Israel, will physically return to this earth. He will then sit on David’s throne and become King of Israel. This is not just poetic language. It will all literally happen. So, Jesus is not only the Saviour; He is also the King of Israel and of the whole world. Moreover, He is going to judge the whole world:
31 “But when the Son of Man comes in His glory, and all the angels with Him, then He will sit on His glorious throne. 32 All the nations will be gathered before Him; and He will separate them from one another, as the shepherd separates the sheep from the goats; 33 and He will put the sheep on His right, and the goats on the left
34 “Then the King will say to those on His right, ‘Come, you who are blessed of My Father, inherit the kingdom prepared for you from the foundation of the world. Matthew 25 31-34 (NASB)