The word "enthusiasm" is defined in the dictionary as "intense and passionate zeal."
I can't think of anything else more important in life than to have enthusiasm.
Here are a few quotes from various writers on the subject.

Nothing great was ever achieved without enthusiasm.
~ Ralph Waldo Emerson ~

The best tool for any job - enthusiasm - makes heavy work lighter.

Enthusiasm is the most beautiful word on earth.
~ Christian Morgenstern ~

Enthusiasm is the most convincing orator; it is like the infallible law of nature. The simplest man, fired with enthusiasm, is more persuasive than the most eloquent man with out it.
~ Unknown ~