Here's why:
* Abstract nouns represent concepts, qualities, states, or ideas that cannot be physically touched or seen.
* Gesture refers to a movement of the body or a part of the body, typically the hands, to express an idea or emotion. While you can see and observe a gesture, the gesture itself is an expression of something more abstract.
For example, you can see someone waving their hand (a physical action), but the gesture itself is an expression of greeting or farewell (an abstract concept).