Gloves are a must for mountain-biking. If you haven't worn them before now you will wonder how you did without them. They help you keep a grip on your bike when things get sweaty, they help protect your hands from blisters and callouses and if they are decent they will have little pads at key points which protect your joints from jarring on those bumpy sections. The open-fingered variety are what you need if you are only riding in summer, but a full-finger glove might be worth considering for those winter rides.