Magistrate's Scepter has at least one charge counter on it.
You are able to play a number of lands this turn equal to four minus the number of charge counters on Magistrate's Scepter.
Steps
Play Orzhov Basilica.
When Orzhov Basilica enters the battlefield, it and Evolution Sage trigger.
Resolve the Orzhov Basilica trigger, returning it from the battlefield to your hand.
Resolve the Evolution Sage trigger, putting a charge counter on Magistrate's Scepter.
Repeat from step 1 until Magistrate's Scepter has four or more charge counters on it.
Activate Magistrate's Scepter's second ability by tapping it and removing three charge counters from it, causing you to take an extra turn after this one.