The speaker says we should glorify God because he has given us dappled, spotted, freckled, checkered, speckled, things. (This poem says "dappled" in a lot of different ways.)
The speaker goes on to give examples. We should praise God because of the skies with two colors, like a two-colored cow. And the little reddish dots on the side of trout. And the way fallen chestnuts look like red coals in a fire. And the blended colors of the wings of a finch (a kind of bird). And landscapes divided up by humans into plots for farming. And for all the different jobs that humans do.
In short, the speaker thinks we should praise God for everything that looks a bit odd or unique, everything that looks like it doesn't quite fit in with the rest.
All these beautiful, mixed-up, ever-changing things were created or "fathered" by a God who never changes. The speaker sums up what he believes should be our attitude in a brief, final line: "Praise Him."