If analysis of the control chart indicates that the process is currently under control (i.e. is stable, with variation only coming from sources common to the process) then data from the process can be used to predict the future performance of the process.
Data from the process can be used to predict the future performance of the process. The process is currently under control (i.e. is stable) then. This is with variation. This is what Analysis of the control chart indicates. This variation is only coming from sources common to the process.