Maintain means to keep the same––keep steady, keep up, or keep going. Sure, you can ride your bike super fast on a flat surface, but it can be hard to maintain that speed, or keep the same speed, going up a hill.
When you maintain a strict study schedule, you stick to it. When you maintain your car in good working order, you take good care of it. If you maintain records of your business activity, it means you make notes of your sales and expenses. If a teacher maintains order in the classroom, she never lets disruptions get out of hand. If you maintain your family, you keep them in food, shelter and clothing. If you maintain that eating animals is cruel, you keep that position.