Written as a series of vows, the poem is a promise of unconditional support. The speaker imagines someone they love at their lowest: on their knees, crying, physically broken, out of hope. Each time, the answer is simple and steady. "I'll stand you back up." "I'll heal you." "I'll be there."
The structure does a lot of the work. Every stanza begins with "And when you," so the troubles pile up one after another, and each is met with the same calm reassurance. The promises also grow. First the speaker offers to lift the person up, then to heal them, and finally just to be present. The last stanza is the most moving, because it admits the other person might push the speaker away, and the speaker stays anyway.
The mood is tender, loyal and quietly determined. The short lines make it feel like someone speaking softly, without drama, simply meaning what they say.