Eyepieces are essential parts of a telescope. With different eyepieces, different zoom levels may be achieved. Eyepieces are interchangeable, and thus, may be used from one scope to another. It is always advisable to invest on a good one, since you may still be able to use it in case you have finally decided to upgrade and buy a new and larger telescope.
New telescopes are usually supplied with 2 eyepieces, one is ‘hi-power’, which will show zoomed-in views, great for close-up views of planets, the other one is a ‘low-power’, which shows zoomed-out views, intended for observing deep-sky objects. Below are eyepieces supplied in one of my telescopes: