The speaker is writing to someone they have hurt, after some shared failure, and the poem is a thank-you for being forgiven. They explain that they laid out their reasons and admitted their shortcomings, even though honesty made it hard to speak. The word "bindings" suggests a mouth held shut by the weight of telling the truth. The other person listened, understood the speaker's faults, and forgave the "tumults" of their hand, which hints at clumsy or impulsive actions. The phrase "saving the guilty from the grave" makes that forgiveness feel almost like a rescue.
The last line shifts the tone. Instead of more explanation, the speaker offers a hydrangea and says their heart is now like it. Judging by the imagery, the flower stands for a heart that has softened, opened, and been renewed. The mood is humble and grateful, quiet and sincere, with relief after a painful conflict. The old-fashioned "thou forgave" adds a touch of reverence.