"I've known her" in line nine hints us that this poem is about a specific woman Dickinson knew. We need to identify her from all the descriptions. Chariots and Emperor are odd in this case, and the key.
The Soul selects her own Society－1
Then－shuts the Door－
To her divine Majority－
Present no more－
Unmoved－she notes the Chariots－pausing－5
At her low Gate－
Unmoved－an Emperor be kneeling
Upon her Mat－
I've known her－from an ample nation－9
Choose One－
Then－close the Valves of her attention－
Like Stone－
Then－shuts the Door－
To her divine Majority－
Present no more－
Unmoved－she notes the Chariots－pausing－5
At her low Gate－
Unmoved－an Emperor be kneeling
Upon her Mat－
I've known her－from an ample nation－9
Choose One－
Then－close the Valves of her attention－
Like Stone－
(F.409/J.303)
[1] Soul selects her:: the Holy Ghost selected Mary. "When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost." (Matthew 1:18) her own Society:: Mary's own society (her family) to accept pregnancy before marriage.
[3] Majority:: the state of being major or of full age (OED 2). divine Majority:: from the birth to the full age of Jesus.
[4] Present no more:: there exists no record of Mary in Jesus' childhood until Jesus was twelve. "And the child grew, and waxed strong in spirit, filled with wisdom: and the grace of God was upon him." (Luke 2:40)
[5] Chariots:: the ride of "wise men from the east." (Matthew 2:1)
[6] low Gate:: the low gate in Mary's house.
[7] Emperor:: a title of sovereignty considered superior in dignity to that of king (OED 3a); indicating Jesus "the King of kings." (1 Timothy 6:15)
[8] kneeling:: Dickinson assumed that the child (Emperor) would kneel to his mother (Mary) before his majority.
[9] I:: the narrator, Dickinson herself. ample nation:: the great Christian world. I've known her:: Dickinson knew the story of Virgin Mary from the Christian world.
[10] Choose One:: a single belief chosen by the Christians.
[11] close, her attention:: the ample nation (Christians) closed her (the nation's) attention to others.
[12] Stone:: a mind hard to change.
I have fought under de Emperor Bonaparte, but now I fight under de Emperor Jesus. ─ The Methodist Review Vol. II (1819)
Yea, let us mark this also by the way, that, as our most valiant Lord and emperor Jesus Christ by his resurrection gat the victory over Satan, sin, death, hell, desperation, and all that is enemy to man's health; ─ The Catechism of Thomas Becon (1844)
but yet none of these, nor indeed all of them, can be compared to the eternal emperor Jesus Christ. ─ A New Universal History of the Religious Rites (1814)
And when they wanted wine, the mother of Jesus saith unto him, They have no wine. Jesus saith unto her, Woman, what have I to do with thee? mine hour is not yet come. (John 2:3-4)