The probable reason your code doesn't work is that it:
a) captures the current setting,


b) turns on track changes,
c) restores the original setting.
So, unless track changes was already 'on' when you started the macro, it would be 'off' again once the macro has finished running. All you need is:
ActiveDocument.TrackRevisions = True
which hardly seems worth a macro - you can achieve the same result by adding the 'track changes' option to the status bar, then clicking on that any time you want to change the state.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

But your suggestion doesn't achieve what I want to achieve besides turning on/off tracking: I want to keep the current revision display setting. If revision display is off, it shouldn't be turned on by switching on/off the tracking; if revision display is on, it shouldn't be turned off by switching on/off the tracking.

The track change option will turn on the revision display as it turns on the tracking.