Or perish from the Hill —
Without the privilege to know
That they are Beautiful —
How many cast a nameless Pod
Upon the nearest Breeze —
Unconscious of the Scarlet Freight —
It bear to other eyes —
F534 (1863) J404
In this sentimental poem, Dickinson reflects on how unaware of their own worth people can be. Some like flowers bloom and perish in the quiet backwaters of Wood and Hill. Did they really not know whether or not they were "Beautiful"? Dickinson wonders if they had "the privilege to know", and in the usage of her day "privilege" here would probably mean the opportunity or chance to know.
I doubt that Dickinson is referring to physical beauty. That's one sort of self knowledge we gain early, unless we are raised in a hermitage. Inner beauty, however, almost by definition is only seen by discerning others. Perhaps Dickinson is imagining a small village with a beautiful soul or two but without anyone who might convince them of that – or perhaps would even notice.
The second metaphor for unseen worth is that of a flower pod carried by a breeze to disseminate its seeds. This is clearly a reference to all the good things – the seeds – planted by simple words and gestures, an act of kindness, years of careful devotion and attention – all the actions that are ultimately nurturing and generative. It is a very feminine image. A good soul casts such pods throughout life without even realizing the effect they have on others.
Because Dickinson specifies the effect of the pods on others as "Scarlet Freight" born to the eyes, it may be that she is (also) talking about poetry. Poems are visual, most times. That Dickinson considers they deliver some heavy freight has been discussed in earlier discussions here and quite extensively elsewhere. I think it likely that the brilliant red maple achene, the samara, is the pod she is visualizing. It's a lovely image: the graceful maple tree dispersing its winged seeds in the breeze. Granted the achenes are not pods, but "Pod" is just such a fine word, I would never quibble with it. (A commenter mentioned a couple of uses of "pod" in recent poems – and here is a third.)
Dickinson touches on a similar theme in "Except to Heaven, she is nought" (F173). In that poem she writes of a small flower that is not valued by any except Heaven and the tiny creatures who benefit from it. I read that poem as a metaphor for a woman, perhaps Dickinson herself. Except to the bees, butterflies and breezes who recognize her beauty and importance, the little flower is "superfluous" and "provincial"; as a result, she is "lone" and "unnoticed".
I don't find the tone in either that poem or this one to be anything but sweetly, wistfully sentimental. There are quiet souls to be appreciated, perhaps in contrast to men like the poet's opinionated father and brother or the well-traveled and lionized men that were her favored correspondents. These men certainly were aware of their "beauty" and the impact of their pods. But doesn't it sound odd to phrase it like that? Our thoughts turn immediately to the housewives who die sad, quiet, early deaths in other Dickinson poems.