It is a colorful bit of writing. We are accustomed to being human, and living everyday lives. Often we get bored and dissatisfied. The writer wants us to appreciate what we have, and to see even the most everyday thing as miracles. He invents a humorous example. It sounds silly, but it isn't. The skin of the human body is wonderfully protective, for example. To give another example, we feel that the human life span is short, and aren't sufficiently grateful for the fact that it is among the longest lifespans of all mammals.

If you are asking what this particular quote means rather that what is a quote in general here is the answer. "does not dissolve in one's bath like a lump of sugar" a lump of sugar will dissolve and disappear very quickly and easily in a bath full of water. This quote is saying that miracles do not disappear that easily.

repeat or copy out (a group of words from a text or speech), typically with an indication that one is not the original author or speaker. "he quoted a passage from the Psalms" synonyms: recite, repeat, reproduce, retell, echo, parrot, iterate; More