The ideal-gas law is the connection between the state variables pressure, temperature, and volume. If the state variables change, as they would from heating or compressing the gas, the state of the gas changes. An ideal-gas process is the means by which the gas changes from one state to another.
NOTE Even in a sealed container, the ideal-gas law is a relationship among three variables. In general, all three change during an ideal-gas process. As a result, thinking about cause and effect can be rather tricky. Don’t make the mistake of thinking that one variable is constant unless you’re sure, beyond a doubt, that it is.