The Alchemist's words are a paraphrase of an ancient idea, perhaps most memorably expressed by William Blake:

The question calls for your personal response, but that response, like many people's, may require some clarification. First, the claim and the question needs to be put more clearly. The Alchemist says that, by contemplating one grain of sand, you can see in it all the marvels of creation. Is this the same as "understanding the universe," the terminology used in the question?

The answer depends on what you mean by "understanding." One of the key qualities of mystical experiences (which renders them so frustrating to non-participants) is that they are generally inexplicable and non-transferable. You might see all the marvels of creation in a grain of sand, but you probably cannot explain to anyone else what you see or how to replicate the experience. Does this constitute understanding? We tend to think, in everyday life, that if someone cannot explain something, they do not understand it. If you understand how light travels in a vacuum, or what causes earthquakes, you should be able to explain these matters.

Whether you agree with the Alchemist, therefore, will depend on your view of mystical, transcendent experiences in general, and perhaps on whether you believe you have ever had such an experience yourself. However, even if you have experienced this way of perceiving the world, you should consider carefully whether this experience constitutes understanding, and whether there is anything in it that you can convey to anyone else.