Sometime too hot the eye of heaven shines,
And often is his gold complexion dimm'd,
And every fair from fair sometime declines,
By chance, or nature's changing course
The sun is sometimes too hot or dim.
Beauty eventually fades
The best paraphrase of the first two lines would be:
Sometimes, the sun shines too bright, but it is often occluded by clouds.
The best paraphrase of the last two lines would be:
Eventually, beauty fades, be it from chance or the passing of time.