You can see, in this dual role given to the Son, that the Father knows Christ is the solution to everything.
We’ve considered the first dramatic statement about Christ in Psalm 110. “The Lord said to my Lord, ‘Sit at My right hand, till I make Your enemies Your footstool’” (Ps 110:1). This is quoted often in the New Testament, especially by the Lord, confounding the Jews. How could David’s Son also be David’s Lord (Adonai)? The verse is inexplicable without acknowledging the complex unity of the Three-in-One God. But now we turn to the second great unveiling. Christ is not only God’s selected King; He is also His appointed Priest. “The Lord has sworn and will not relent, ‘You are a priest forever according to the order of Melchizedek’” (v 4). With both declarations, we mere mortals are listening in on communications between the Father and the Son, just as we have in John 17. What holy ground! This truth was a biblical bombshell. How carefully God had crafted Israel’s government to separate the kingship and priesthood. The kings were from Judah (Saul excepted), the priests from Levi, and never the twain shall meet. There were many king-priests in the pagan world, but Melchizedek was a “priest of the Most High God” (Heb 7:1). His priesthood wasn’t Levitical, based on the law, but established entirely on God’s grace. It was not an afterthought, for his priesthood pre-dated the Aaronic priesthood, and will long outlive it as well, for Christ is “a priest forever.” What does a Melchizedek priesthood do, for sacrifice is not mentioned— Christ’s once-for-all sacrifice has been made. Once our King-Priest has put down all rebellion (vv 5-6), like Melchizedek, His ministry will be one of fellowship, blessing, and encouragement. “He shall drink of the brook by the wayside; therefore He shall lift up the head” (v 7).