Dave Bonta's short poem sets two small, strange ideas side by side. In the first couplet, ice and water trade places "like a parliament of one." Ice becomes water, water becomes ice, and the days swap with them. The odd image of a parliament with only one member suggests a debate happening inside a single mind, or a single substance, arguing with itself and always reaching the same split decision: change.
The second couplet turns inward. The speaker says doubt will give "a new home" to whatever they believe is true. That's a quietly surprising idea. Doubt usually threatens belief, but here it becomes a kind of shelter, a place where belief can go on living in a different form.
The title, "Complementarity," ties the two halves together: opposites that need each other. The mood is calm, thoughtful and a little puzzled. The speaker doesn't seem upset by uncertainty, just open to it, willing to let beliefs melt and refreeze like the ice and water.