A helmet is to protect your face and gloves protect your hands so you do not cut your hands. Do you know what to do with armour? It is to protect your heart. Elbow pads protect your elbows.
Your bike can get dirty and you have to wash your tyres because the dirty tyres will slow you down when you go up the hills and even if you go down a hill even if you go on flat ground you slow down.
You do not want to get the wobbles going up the jump or you will hit the ground and it hurts like when you get bucked off a horse! You can fall off and break a bone and that hurts!