Franklin’s (1998) punctuation and ED’s alternate words in parentheses:
The Spirit is the Conscious Ear —
We actually Hear
When We inspect—that’s audible—
That is admitted—Here—
For other Services (purposes)—as Sound —
There hangs a smaller (minor) Ear
Outside the Castle (Centre, City) —that Contain (Present)—
The other —only—Hear—
Here’s my interpretation, using ED’s alternate words when they help and my clarifications in brackets. Lines 1-3 are enjambed into a single sentence, and Line 4 is a single sentence. Lines 5-7 are also enjambed into a single sentence, and Line 8 is a closing sentence.
The Spirit is the Conscious Ear
We actually Hear
When We inspect [what’s] audible— [in our soul].
That [song] is admitted—Here—[in the Conscious Ear].
For other Purposes—such as Sound [physical sounds such as bird songs]—
There hangs a minor Ear, [the physical ear]
Outside the Castle [of our soul, which] Contain[s] the [Conscious Ear].
The other [the minor ear] only Hear[s] [physical sounds].
In a footnote to this poem, Christine Miller (2016, ‘Emily Dickinson’s Poems’) refers readers to ‘Ode on a Grecian Urn’ (John Keats, 1819, Stanza 2):
“Heard melodies are sweet, but those unheard
Are sweeter; therefore, ye soft pipes, play on;
Not to the sensual ear, but, more endear’d,
Pipe to the spirit ditties of no tone”
Given ED’s interest in “the spirit ditties of no tone”, that is, mystical experiences, her “Conscious Ear” is the one that hears God speaking, the “Ear” Saul used to listen to God on the road to Damascus (KJV, Acts 9:3-5):
3 As he journeyed he came near Damascus, and suddenly a light shone around him from heaven.
4 Then he fell to the ground, and heard a voice saying to him, “Saul, Saul, why are you persecuting Me?”
5 And he said, “Who are You, Lord?” Then the Lord said, “I am Jesus, whom you are persecuting. . .”
It would be hard for any poet, including ED, to improve on Keats. To me, ED’s “Ear” / “Hear” / “Here” // “Ear” / “Hear” sound clunky compared to Keats’ “Heard”, “unheard” // “ear”, “endear’d”.