We must not squander our power, helplessly and ignorantly, squirting half the house in order to water a single rose-bush (1).”

I was thinking that this quote means to focus on one thing at a time. Is there anything else I am missing from it. It's from Virginia Woolf; essay "how should one read a book?"

Yes, I agree with your interpretation. It may help to read the entire sentence, indeed the entire essay.

"To enjoy freedom, if the platitude is pardonable,
we have of course to control ourselves.
We must not squander our powers,
helplessly and ignorantly,
squirting half the house in order
to water a single rose-bush;
we must train them, exactly and powerfully,
here on the very spot."

http://www.for68.com/new/2006/7/sw1155292558102760029744-0.htm

The quote you provided is indeed from Virginia Woolf's essay "How Should One Read a Book?" It expresses the idea of not wasting our energy and resources on tasks that are insignificant or inefficient.

While your interpretation of focusing on one thing at a time is valid, there are a couple of additional aspects worth considering in relation to this quote:

1. Conservation of resources: The analogy of "squirting half the house" implies a wasteful usage of water. Likewise, Woolf suggests that we should be mindful of how we use our personal power or energy. Instead of dispersing it ineffectively, we should direct it towards meaningful and relevant endeavors.

2. Knowledge and understanding: Within the context of Woolf's essay, this quote can also be seen as emphasizing the importance of deep reading and dedicated engagement with a book. It encourages us not to skim through a text or approach it superficially, but to focus our attention and fully immerse ourselves in the reading experience. By doing so, we can obtain a richer understanding and extract more value from the book.

In summary, along with the idea of focusing on one thing at a time, the quote also highlights the importance of conserving our personal resources and investing them wisely. Additionally, it suggests the significance of dedicated and immersive reading for a deeper understanding of a book's content.