Rehearse is one of those words that can go either way, it all depends on the context in which it was used. You can rehearse a past event or story so as to celebrate or commemorate what DID happen. But you can also rehearse so as to prepare or practice for some future event that WILL happen. Or, I suppose, it is entirely possible that it could be both, looking back and looking forward.
For instance, in Leviticus 23:3 God institutes the Sabbath, or in Hebrew, Shabbat, which means to cease. It certainly looks back to creation, six days of creating and a day of rest. It's very celebration can be a reminder, rehearsal, that God worked six days and then took a break. But it can also be a rehearsal for us to take a break once in a while...every seventh day, this week, next month, next year.
Verses 1 & 2 make it clear that the reason we are to "rehearse" the Sabbath or Shabbat is to proclaim it, show the world, set the example by rehearsing what was and what is to be.
Stand by, there are 7 more feasts or holidays Israel was to rehearse so as to proclaim...