If you don't know what a checkpoint is, check out our getting started article. This article also assumes you've configure WebSphere to automatically create Delta checkpoints when a change is made to the master configuration.
Often, you don't know what changed in the master configuration. This is where checkpoints can be quite handy. In the WebSphere admin console, at System administration > Extended Repository Service > Repository Checkpoints, you can select a Delta checkpoint and select Export.
This will export a ZIP file to your local PC. The contents of the ZIP file are dead give away, letting you know the type of change that was made to the master configuration.