The speaker is stuck on a question that has no answer: how do you measure a life? Breath, flame, soul and ash all slip past any scale. The body hides them, and the speaker admits they can't turn themselves inside out to look. Even death offers no clear reading, since the lifeless body simply disappears into earth, sky and the other elements, quietly.
In the second part, the speaker turns to the unseen "thread" that holds life together, whether now or after death, and says there is no way to know how it works. The image of colour on tree leaves is striking: colour has no real weight, so if we can't feel even that, how could we feel a life's? The closing words, "shrinking into itself," leave it unclear whether the leaves, the life or the thought itself is withdrawing.
The mood is quiet, uncertain and a little humbled. The speaker doesn't panic or argue. They simply accept how little can be known.