The LORD says to my Lord: "Sit at my right hand until I make your enemies a footstool for your feet." The LORD will extend your mighty scepter from Zion; you will rule in the midst of your enemies. (Psalm 110:1-2)
The LORD has sworn and will not change his mind: "You are a priest forever, in the order of Melchizedek." (Psalm 110:4)
While the Pharisees were gathered together, Jesus asked them, "What do you think about the Christ? Whose son is he?"
"The son of David," they replied.
He said to them, "How is it then that David, speaking by the Spirit, calls him 'Lord'? For he says, " 'The Lord said to my Lord: "Sit at my right hand until I put your enemies under your feet." '
If then David calls him 'Lord,' how can he be his son?" No one could say a word in reply, and from that day on no one dared to ask him any more questions. (Matt 22: 41-46)
It's pretty clear that both the Lord and the Pharisees he was addressing believed that Psalm 110 referred to the Messiah and that the Holy Spirit had inspired King David to write it. Where they differed was in their understanding of the Messiah's origins. The Pharisees believed he would be a human descendant of King David, and nothing more. The Lord knew He was also God in the flesh, and quoted Psalm 110 to remind them that David knew this too.
Many translations show the first appearance of Lord in Psalm 110 all in caps (LORD) and the second one in lower case except for the first letter (Lord). This is to show that David was writing of a conversation he overheard, through the power of the Holy Spirit, between the Father and the Son.
There are two facts to support this conclusion. First, Lord is a title one uses in addressing a superior, and only two were superior to the King. One was God the Father, represented by LORD and the other was God the Son, called Lord. In effect Jesus reminded the Pharisees that David would have referred to a merely human descendant as his son, not as his Lord.
And second, in Hebrew the "word" translated LORD is YHWH, the four initials of the unpronounceable name of God, and used only of Him, while the one translated Lord is a different word, Adonai.
Responding truthfully to the Lord's question would have forced the Pharisees to agree with David, something they weren't prepared to do. Not then, not ever. At His trial before the Sanhedrin, the Lord's declaration that He was the Messiah and that they would all see Him seated at the right hand of the Mighty One and coming on the clouds of Heaven is what stirred them to convict Him of blasphemy, a capital crime. (Matt. 26:64)
Their only problem was that the Romans wouldn't let them execute anyone without permission. So they took him to Pontius Pilate. Pilate wasn't concerned about the charge of blasphemy. That was an internal matter among the Jews. But in calling Himself a King (John 18:33-37), Jesus was confessing to treason under Roman law, also a capital crime (Matt.27:11). Even then Pilate was inclined to release Jesus, but when the crowd became adamant, he saw a way to yield to their wishes while remaining within Roman Law. That's why he had them place a sign on the Lord's cross that said, "Jesus of Nazareth, King of the Jews." He was announcing that the crime for which Jesus was being executed was treason.
King Jesus, Our High Priest
David had written that the Messiah would be both a king and a priest just like Melchizedek had been. From Genesis 14:18 we learn that Melchizedek, whose name means King of Righteousness, was both a priest of the Most High God and the King of Salem, a Jebusite city that later became known as Jerusalem. When David conquered the Jebusites he made Jerusalem the capital of Israel, and purchased the land on nearby Mount Moriah where Abraham had sacrificed Isaac several hundred years earlier for the Temple location.
Never since the founding of Israel had one man been both a king and a priest. It was forbidden. Kings came from the tribe of Judah, while priests were descended from Levi. One king who tried to function as a priest earned the Lord's immediate displeasure, and serves to illustrate the point. Daring to offer incense in the Temple, King Uzziah immediately contracted leprosy and was quarantined till his dying day (2 Chron. 26:16-21). Some prophets were also priests, Ezekiel and Zechariah for example, and David was a king and a prophet. But no one was ever both a king and a priest in Israel.
However, prophecies in Ezekiel 21:25-27 and Zechariah 6:9-13 tell us the two offices will eventually be united when Messiah comes and that He will be both a king and a priest. And of course in the Book of Hebrews Jesus is called our King (Hebr. 1:8) and Our High Priest (Hebr. 4:14). This is possible because Jesus is not a priest in the Levitical sense but in the higher order of Melchizedek. All of Hebrews 7 is devoted to this topic.
I Know I Am But What Are You?
In Exodus 19:6 Israel is called a kingdom of priests but in 1 Peter 2:9 we read, "But you are a chosen people, a royal priesthood, a holy nation, a people belonging to God, that you may declare the praises of him who called you out of darkness into his wonderful light." He was speaking to the Church, calling us a royal priesthood. Only kings are considered royalty.
And in Revelation 1:5-6 it's even clearer. And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth. Unto him that loved us, and washed us from our sins in his own blood, and hath made us kings and priests unto God and his Father; to him be glory and dominion for ever and ever. Amen. (KJV)
Some of the modern translations prefer the word kingdom over kings in the passage above, and it's true, the Greek word there can be translated either way. They try to compare the Revelation passage with Exodus 19:6 to bolster their replacement theology bias, making the Church look like Israel. But to most conservative scholars it's clear that both the context and the grammatical structure of the passage require that the Greek word be translated kings. (The same is true in Revelation 5:10 where the same phrase is repeated.)
Kings Of What?
The Bible doesn't have a specific answer for this, but in Ephesians 2:6-7 Paul wrote, "And God raised us up with Christ and seated us with him in the heavenly realms in Christ Jesus, in order that in the coming ages he might show the incomparable riches of his grace, expressed in his kindness to us in Christ Jesus."
The "coming ages" alludes to the time of the Millennium and beyond where we'll serve as living examples of the incomparable riches of God's grace, seated with our King and High Priest on His throne.
Throughout human history the best kings have always been the ones most sincerely devoted to the wellbeing of their subjects. And the priests were not just religious officials. In most generations they were their society's repository of knowledge in philosophy, literature, religion, art, music, history and language. If these can serve as worldly models of our heavenly future, then we can assume there's a lot more to being a king and a priest than sitting on a throne or conducting a worship service.
In the USA we don't have a royal family so many of us don't know what that's like. But people from other countries do, and they know that for the most part, "royals", as they're called, don't work. Many of them don't even help run the countries their families rule. They follow a higher calling, pursuing personal interests and living lives of service. They have no need to support themselves, so they're free to devote all their time, energy, and intellect to the things they find to be the most fulfilling.
On Earth we all have a sin nature, so we can be drawn off the path of righteousness, and we've seen that happen with many royals. And because of our fallen nature even the best of us can only achieve a small percentage of our nearly limitless potential. But in our perfected state, these things won't be a problem. We'll discover that God created us with capabilities we've barely used. Now we're like a thoroughbred race horse that has been consigned to pulling a child's cart. But all that will change forever at the rapture. Finally there will be nothing to prevent us from achieving our full potential in any undertaking we can imagine.
Both Paul (1 Cor. 15:42-44) and John (1 John 3:2) made it clear that we won't know in advance exactly what we'll be like after the rapture/resurrection. Our motives, our capabilities, and our appearance may all be different. But they both said we'll be like Jesus. That means whatever we do will be pleasing to God and done for His glory. We can only speculate about the specifics.
Does all this exceed the limits of your imagination? Of course it does. That's why Paul called it "the incomparable riches of His grace." He also said, "No eye has seen, no ear has heard, no mind has conceived what God has prepared for those who love him" (1 Cor. 2:9). Having been there and seen our future (2 Cor. 12:2-4) he knew it was beyond the ability of our sin-contaminated minds to imagine. But know this. Being both a king and a priest will be by far the most rewarding, fulfilling calling we've ever had.