What does this quote mean?

"iron rust from disuse, stagnant water loses its purity, and in cold weather becomes frozen; even so does inaction sap the vigors for the mind.""iron rust from disuse, stagnant water loses its purity, and in cold weather becomes frozen; even so does inaction sap the vigors for the mind."

It’s a good idea before reading a long report, such as a government document, to scan headings, because they serve as road signs to guide you.

Explanation:

Headings are used as a presentation of the main idea of each one of the sections in a written work, they are used in long readings since they help reader identify each section and its content without having to read part that may not be necessary at the moment, then the correct word to complete the sentence is headings.