That Title is made up of two Hebrew words which mean 'King of Righteousness’ or 'King of the Just' i.e. King of the Zadok;

 

Heb.7:2.  To whom also Abraham gave a tenth part of all: first being by interpretation king of righteousness, and after that also king of Salem, which is, king of peace.

 

That's who our Lord Christ Jesus will be KING over, i.e. the 'just', and they are His elect priest servants of...

 

 Revelation 20: Read All.

 

 Which reign with Him in The LORD's House for that "thousand years".
     How does one become one of the 'just' servants of Christ? Do what verse 9 says above; with your spirit seek The LORD early, meaning right now! Don't wait until you think you can stop sinning, or until the time of tribulation is upon us. Seek The Father through our Lord Jesus now.
     Is there a deeper analogy here in Isaiah 26 with the 'just' (Zadok) who 'wait' for The LORD's return? No doubt, there is. Zadok, one of two priests who served during David's time, stayed true to God's anointed servant, 'king' David.

 

Luke 1:32. He shall be great and shall be called the Son of the Highest: and the lord God shall give unto Him the throne of his father David.

 

Genesis 49:10. The sceptre shall not depart from Judah, nor a lawgiver from between his feet, until Shiloh come; and unto Him shall the gathering of people be.

 

 The throne of David is reserved for our Lord Christ Jesus. Also, as written in;

 

 Acts 13:22: And when He had removed Him, He raised up unto them David to be their king; to whom also he gave testimony, and said, ‘I have found David the son of Jesse, a man after Mine own heart, which shall fulfil all My will.

 

1 Samuel 13:14. But now the kingdom shall not continue: the lord hath sort Him a man after his own heart, and the Lord hath commanded him to be captain over His People, because thou hast not kept that which the Lord commanded thee.

 

God said He found David a man after His own Heart. David did all that was commanded of him by God, and erred only in the matter of Uriah .

 

1 Kings 15:5. Because David did that which was right in the eyes of the Lord, and turned not aside from anything that He commanded him all the days of his life, save only in the matter of Uriah the Hittite.

 

Thus King David is the only just example of a ruler born flesh that was perfect in his heart towards God, and his throne is symbolic of Messiah's eventual Eternal reign. Finally then, Zadok, the priest who stayed with David, is symbolic of those 'in Christ' today who will not be deceived, and will "wait" for His coming, instead of falling away to the false king who will come first. Those who are deceived and fall away are symbolic of the priest Abiathar, which later turned to the false king Adonijah, David's fourth son. Adonijah attempted to set himself up as king when David was old.

 

 1 Kings 1:1-8. Read All.