The speaker is describing a woman, and the admiration comes through right away: "surely a work of art that one." The poem then builds that idea through a painting metaphor. On the outside, she looks like "violent slashes and thrown paint," which suggests someone who may seem harsh, messy, or intense at first glance. Inside, though, she is "billions of delicate dots and soft strokes," a much quieter and more careful kind of picture.
The point seems to be that appearances mislead. The wild surface and the tender interior don't cancel each other out. They come "together" to make one story, and the poem calls that story "silent" and "painted." That word choice hints that she may not tell it in words, so you have to look closely to understand her. The mood is warm and respectful, with a touch of wonder. The speaker doesn't judge the rough exterior but treats it as part of the beauty, as if the whole person, contradictions included, is the artwork.