@ Eliakim as a type of Christ:
And it shall come to pass in that day,
that I will call my servant Eliakim the son of Hilkiah:
And I will clothe him with thy robe,
and strengthen him with thy girdle,
and I will commit thy government into his hand:
and he shall be a father to the inhabitants of Jerusalem,
and to the house of Judah.
And the key of the house of David will I lay upon his shoulder;
so he shall open,
and none shall shut;
and none shall open.
And I will fasten him as a nail in a sure place;
and he shall be for a glorious throne to his father's house.
Isaiah 22:20-23
****What about that "shoulder"?....For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: Isaiah 9:6
****He is given the kingdom after the Judgment....Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it with judgment and with justice from henceforth even for ever. Isaiah 9:7
****We see this in Daniel....But the judgment shall sit,....And the kingdom and dominion, and the greatness of the kingdom under the whole heaven, shall be given to the people of the saints of the most High, whose kingdom is an everlasting kingdom, and all dominions shall serve and obey him. Daniel 7:26,27
@ The 3 Doors of the Sanctuary:
1- Outer Court
2- Inner Court (Holy Place)
3- Most Holy Place
****When is the key used?....And to the angel of the church in Philadelphia write; These things saith he that is holy, he that is true,
he that hath the key of David,
he that openeth,
and no man shutteth;
and no man openeth;
I know thy works: behold,
I have set before thee an open door,
and no man can shut it:
Revelation 3:7,8
* It is used during the Church of Philadelphia, right before the 7th Church which is Laodicea.
@ Which Door in the Sanctuary in Heaven is it for?
First Door: Opened at His incarnation leading to the altar of Sacrifice in the Outer Court.
It was here on earth where He was offered on the Cross & also where He was physically baptized. (Altar of Burnt Sacrifice & Brazen Laver).
Second Door: Opened at His ascension. John saw this door already open- After this I looked, and, behold, a door was opened in heaven: and the first voice which I heard was as it were of a trumpet talking with me; which said, Come up hither, Revelation 4:1......This was the Inner Court. John would go on to see the candlestick & altar of incense which is in the Inner Court.
Third Door: And the temple of God was opened in heaven, and there was seen in his temple the ark of his testament: Revelation 11:19 Here we see the Most Holy Place, for the ark of the covenant is there. And of course, here was where the Judgment (Day of Atonement) took place upon the entrance of the High Priest. This is also at the beginning of the 7th trumpet which of course the end of the 6th. In other words, between the 6th Church (Philadelphia) & 7th Church phase (Laodicea).
SUMMARY:
The Key of David was used for opening the 3rd Door in the Sanctuary, (Most Holy Place) for the Judgment, following of which His Father will give Him His Kingdom & then the government will be upon His shoulder.