You control two additional Cleric creatures with different mana values.
An additional Cleric creature card in the graveyard with a higher mana value than the other two.
Steps
Activate Whisper using its own ability by tapping it and sacrificing your two additional Cleric creatures.
Whisper's ability from Thornbite Staff triggers twice and Orah triggers twice, but one of Orah's triggers has no valid target.
Resolve one Whisper trigger, untapping Whisper.
Resolve Orah's trigger, returning the sacrificed Cleric with the lowest mana value from your graveyard to the battlefield.
Resolve Whisper's ability, returning the Cleric with the highest mana value from your graveyard to the battlefield.
Activate Whisper using its own ability by tapping it and sacrificing your two additional Cleric creatures.
Whisper's ability from Thornbite Staff triggers twice and Orah triggers twice.
Resolve one Whisper trigger, untapping Whisper.
Resolve both Orah triggers, returning two Cleric creatures from your graveyard to the battlefield.
Resolve Whisper's ability, returning any creature from your graveyard to the battlefield.
Repeat any number of times.
Once you have no non-Cleric creature cards in your graveyard, you may choose the same Cleric with both Orah triggers in step 7 to avoid running out of valid Whisper targets, or you may sacrifice a non-Cleric creature to Whisper.
Resolve all Whisper triggers from the Thornbite Staff ability, untapping Whisper any number of times.
Results
Infinite blinking of non-Whisper creatures you control and creatures in your graveyard.
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinite sacrifice triggers.
Return all creatures from your graveyard to the battlefield any number of times.