How can Jesus be both root and offspring of David if he was only a man and did not pre-exist his incarnation?
This is an important question. It deserves to be answered from biblical facts which God has abundantly provided - there is no need for assumptions. Before answering, we do need to rehearse the solid foundation provided regarding Jesus.
He will be great and will be called the Son of the Most High; and the Lord God will give him the throne of his father David; 33and he will reign over the house of Jacob forever, and his kingdom will have no end.” 34But Mary said to the angel, “How will this be, since I am a virgin?” 35The angel answered and said to her, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; for that reason also the holy child will be called the Son of God". Luke 1:32-5
Is Jesus mentioned as a living person before his conception? No. Should we assume he does pre-exist based on invented stories appearing 100's of years after the Apostles which none of God's inspired writers affirm? The Gospels tell us when and how Jesus arrived, are consistently unambiguous and affirmed by several biblical authors. We either believe them at face value or choose alternate sources.
We have several prophecies recorded for us of the 'one to come'. Abraham, 'saw Jesus' day and was glad', John 8:56. David called Jesus his Lord and understood that God would place his descendant on his throne (2Samuel 7:12 13,16, Ps 132:11, 89:3-4). Even prophesying his Lord's life and death Ps 22 - even though he could not grasp the significance of his very specific details.
God of armies, do turn back; Look down from heaven and see, and take care of this vine, 15The shoot which Your right hand has planted, And of the son whom You have strengthened for Yourself. 16It is burned with fire, it is cut down; They perish from the rebuke of Your face. 17Let Your hand be upon the man of Your right hand, Upon the son of man whom You made strong for Yourself. Ps 80:14-17
- A pointer to Jesus ascending to God's right hand - the man God was going to strengthen to do the job He sent him to do - be the saviour of the world and the "Lord" David wrote about, Ps 110.
- Abraham was also advised his descendant would bless the world. Paul also understood where Jesus came from, Gal 3:16
In your (Abraham) seed all nations of the earth shall be blessed, Gen 22:18
For those who believe Jesus did not pre-exist his incarnation, How can Jesus be the root of David if he is David's offspring?
What incarnation? Where do we read about this fanciful idea? The bible contains no story or prophecy about God becoming a man. All we have is a few proof-texts used to push in that direction when read out of context. Or from doubtful translations that have allowed a bias (not intended by God) to alter the scriptures.
Did you notice this bit from the first quotation?
the Lord God will give him the throne of his father David.
- the Lord God will give him... God is giving to who? To God aka Jesus? Why is God giving the throne to God? Did God somehow deserve this reward?
- the throne of his father David. Seems pretty straight forward. God doesn't have a father - certainly not David. But Jesus does have David as a great, great, great... grandfather. One of the gospels affirms this.
- Traditionally, Jesus is God, but this concept doesn't sensibly fit with the clear details provided.
Now how is Jesus the root of David?
God has planned for Jesus to be Saviour from the foundation of the world. Did he already exist back then? No, he was born ~4BC. He is the 'logos became flesh' - same event explained in the gospels. Jesus' name is his identifier. Just as David and Moses and all the other prominent figures had names that identified them and we can trace them through the pages of the bible. Jesus is not mentioned until his conception and birth. He was spoken about prophetically, because his time was not yet.
God, after He spoke long ago to the fathers in the prophets ... 2 in these last days has spoken to us in His Son, whom He appointed heir of all things... Heb 1:1-2
But when the fullness of the time came, God sent His son, born of a woman, born under the Law. Gal 4:4
Nothing about God being born out of a woman or a pre-existing Son who is also God or an incarnation - just a simple birth from a virgin God had chosen to birth His Messiah. We can read-in all that other stuff, but why do we need to? There is no need to presume, if God sent His son, he must have pre-existed! Sending His son is making Mary pregnant! As the gospels tell us over and over without any mystery or complexity.
God has planned everything to happen in a way that leads predictably to the ultimate 'end game'. He has put in place a plan for man's salvation and it is working perfectly. Jesus is the cornerstone of that plan.
you are no longer strangers and foreigners, but you are fellow citizens with the saints, and are of God’s household, 20having been built on the foundation of the apostles and prophets, Christ Jesus himself being the cornerstone, 21in whom the whole building, being fitted together, is growing into a holy temple in the Lord, 22in whom you also are being built together into a dwelling of God in the Spirit. Eph 2:19-
Jesus, the one planned to come, needed a beginning. Not just a birth, but a heritage, a lineage of grand proportions, of righteous men and women who faithfully served God in very demanding situations. God planned for Jesse to be the father of David whose throne Jesus would make endure forever.
1Then a shoot will spring from the stem of Jesse, And a Branch from his roots will bear fruit. 2The Spirit of the LORD will rest on him, The spirit of wisdom and understanding, The spirit of counsel and strength, The spirit of knowledge and the fear of the LORD. 3And he will delight in the fear of the LORD, And he will not judge by what his eyes see, Nor make decisions by what his ears hear; 4But with righteousness he will judge the poor, And decide with fairness for the humble of the earth; And he will strike the earth with the rod of his mouth, And with the breath of his lips he will slay the wicked. 5Also righteousness will be the belt around his hips, And faithfulness the belt around his waist. Isaiah 11:1-5
Being the root of David is the manner by which God had prepared for Jesus' lineage. This holy stock of humanity from which Jesus came. These men and women were set aside for God's purposes - they are the ROOT from which came God's son Jesus. The prophecy of Jesus coming is self-fulfilling - it has it's root in all those God had prepared until Jesus was born.
Then on that day the nations will resort to the root of Jesse, Is 11:10
This is simply a case of God knowing the beginning from the end - Jesus is reason for all that would complete events according to God's sovereign plan. Jesus, the chief cornerstone was planned before the world began.
Jesus is the reason for Jesse! For David and everyone that was part of his story.
for in him all things were created, both in the heavens and on earth, visible and invisible, whether thrones, or dominions, or rulers, or authorities—all things have been created through him and for him Col 1:16
Truly in Jesus all things are held together. Without his saving sacrifice and exalted ascension, nothing would have any meaning. No one would know true life. God's creation would simply cease to exist - it would have no purpose.
Jesus is the root from which all creation flourishes. Not because he made anything, but because he has redeemed everything from evil and sin and death - just as God planned he would. Just as God planned who he would come from and when.
I Jesus have sent mine angel to testify unto you these things in the churches. I am the root and the offspring of David, and the bright and morning star. - Rev 22:16
We read this and we think of Jesus saying, 'before Abraham was, I am'. It all makes perfect sense without reading in anything or jumping to false conclusions. Jesus was before Abraham as being the key, the cornerstone, the reason, the purpose for all things. Abraham was a much smaller part of that plan - of course Jesus was before in the sense of priority and importance - no pre-existence required!
He raised up David to be their king, concerning whom He also testified and said, ‘I have found David, the son of Jesse, a man after My heart, who will do all My will.’ 23From the descendants of this man, according to promise, God has brought to Israel a Saviour, Jesus. Acts 13:22-3