The poem builds like a chain of small arguments, each one leaning on the last. It starts with a plain claim: skies don't lie. But the wind moves the clouds, and the clouds keep changing shape, so what we see up there can't be trusted for long. By the fourth line the speaker flips the opening statement and admits that skies do lie, and the reason is surprisingly human: we exhale. Our breath becomes part of the weather, part of the change.
The ending turns inward. "Keep your water, / Inside your sea" reads like advice, gentle but firm. Judging by the imagery, the water might be tears or feeling, and the sea a person's inner self. The speaker seems to be saying: don't let it all spill out, and don't let the world's shifting surfaces unsettle you. The mood is quiet, reflective, and a little guarded, like someone offering a calm warning in very few words.