What does it mean that Jesus is both Jehovah and Elyon?
Jesus is both Jehovah and Elyon because He is the LORD of the Old Testament and the Most High God, the possessor of heaven and earth. In Matthew 28:18 He claims all power in heaven and earth, matching the title Most High God used of Jehovah in Genesis 14.
Les explains that in Genesis 14, Abram is blessed by the Most High God, the possessor of heaven and earth. When the text uses LORD in all capitals, that identifies Jehovah. So the title "Most High God" is connected with Jehovah. Then in Matthew 28:18, Jesus says all power is given unto Him in heaven and in earth, making Him the possessor of heaven and earth. Therefore He is not only the Jehovah of the Old Testament, but He is also the Elyon, the Most High.
And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth.
And Abram said to the king of Sodom, I have lift up mine hand unto the LORD, the most high God, the possessor of heaven and earth,
More Questions
How does Jesus claim to be the possessor of heaven and earth in Matthew 28:18?
In Matthew 28:18, Jesus alludes to the title 'possessor of heaven and earth' by saying that all power is given to him in heaven and in earth.