msp430 using Button as switch
Eh, most likely you are using a rev1.5 Launchpad. The external pullup pin for the p1.3 button is not populated. Since it is not populated, there is no steady state change. You must enable the internal pullup.

Instead of pinMode(buttonPin); use pinMode(buttonPin, INPUT_PULLUP);

Also, you are trying to read the wrong pin.

Instead of reading = digitalRead(ledPin); use reading = digitalRead(buttonPin);