Why is a space suit important?

Because in space humans would quickly dehydrate and be unable to breath, because 'space' is a near vacuum. Vacuums don't like to be empty, and want to fill up. So they take anything from anywhere to fill the vacuum, and that included human breath and moisture.

Without breath and moisture we would die instantaneously.

Hence the Space Suit, which is impervious to the loss of moisture and air.