The prophecy of Gabriel to Mary in Luke 1:30-33 is an interesting one for amillennialists.
The angel said to her, "Do not be afraid, Mary; for you have found favor with God. "And behold, you will conceive in your womb and bear a son, and you shall name Him Jesus. "He will be great and will be called the Son of the Most High; and the Lord God will give Him the throne of His father David; and He will reign over the house of Jacob forever, and His kingdom will have no end."
Every evangelical amillennialist takes the first part of this prophecy literally. They believe that a literal young lady will literally become pregnant and will have an literal son, who will literally be named Jesus. (If you deny this, you are not an evangelical.)
But then these same evangelical amillennialists take a strange turn when they deny that this literal son literally named Jesus born to a literal young woman will literally rule on the throne of David over the house of Jacob.
They suddenly resort to a spiritual interpretation that the throne of David (which historically was in Jerusalem) is now found in the heart of believers everywhere, and that that house of Jacob (which in the Old Testament was unquestionably a reference to the ethnic descendants of Jacob) is now an amalgamation of people from every tribe, tongue, people, and nation.
The only thing I cannot figure out is why they make this sudden change in hermeneutics. There is no textual reason to make a change, and no necessary theological reason. Mary certainly would not have understood some type of spiritual kingdom.
This sudden switch, as best as I can tell, arises, not from the text, but from a precommitment to not having a literal fulfillment of this prophecy.
But why this precommitment? That is what I have never understood.