They say that "Time assuages"

They say that "Time assuages"--
Time never did assuage--
An actual suffering strengthens
As Sinews do, wih Age--

Time is a Test of Trouble--
But not a Remedy--
If such it prove, it prove too
There was no Malady-
(F 861)

This poem carries a lot of parable elements to it. It plays upon the familiar adage "Time heals all wounds," but changing the saying perceptibly. Rather than time healing, it instead strengthens the body to stand against the wound. There is a subtle distinction in the phrase "an actual suffering", and I think this was Dickinson toying with double or layered meanings.

On one hand, the speaker could be implying that any injury that is inflicted is only significant if time cannot heal it. In other words, pain that one quickly recovers from is perhaps not truly pain. And perhaps "an actual suffering strengthens" can mean that pain can continue to grow and build throughout life, possibly that pain can even be nourished by those who suffer it. Certainly both interpretations could be equally valid.

The final stanza is intriguing because it lacks any real conclusion. The reader must decide for him or herself what to make of the parting words. In this stanza the speaker seems to say that time is the ultimate test, but the test does not conclude or cure the suffering or pain. And the final lines seem to imply that if a cure is found, then there was no real hurt to begin with.

Overall, the poem could be much like a description of broken bones. In time, the break never goes away. It heals over, stronger than before, reinforced better than the bone originally was. And yet the little extra calcium will always be there. Without that bit of extra bone where the break healed, a broken bone would never have existed.