I made slow Riches but my Gain — Freckles

"I've got more freckles, since you saw me," wrote Dickinson to Mrs. Samuel Bowles, and "our freckled bosom bears it's friends" to Mr. Samuel Bowles. The word freckle appears two times in her letters, and seven times in her poems.

What the poem tries to say behind the freckles is usually hidden in words unnecessary to the answer. Night is the time one can shun the sun, the glory. Sun is "sometimes identified with various gods" _{(OED 1c)}. Sum is "the ultimate end or goal; the highest attainable point _{(OED 13a)}. Dickinson did not benefit from the sun and the sum of the sun, like freckles.

I made slow Riches but my Gain ¹
Was steady as the Sun
And every Night, it numbered more
Than the preceding One

All Days, I did not earn the same ⁵
But my perceiveless Gain
Inferred the less by Growing than
The Sum that it had grown.

(F.947/J.843)

[1] slow Riches:: freckles that grow slowly.
[2] Sun:: a hint on sun spot, freckle. steady as the Sun:: the exposure to sunshine steadily increased the freckles.
[3] numbered:: the gain is countable, contrary to the perceiveless gain in line 6.
[6] perceiveless Gain:: the benefit one cannot sense and count.
[7] the less by Growing:: this benefit decreases as freckles growing.
[8] Sum:: a pun on sun, the Sum grows by the Sun.

Ephelis. A sun spot. A solitary, or aggregated spot, attacking most commonly the face, back of the hand, and breast, from exposure to the sun. ─ Medical Dictionary (1829)