Here's why:
* Subordinating conjunctions connect a dependent clause to an independent clause.
* Dependent clauses cannot stand alone as a complete sentence.
* Independent clauses can stand alone as a complete sentence.
In this case:
* Independent clause: The judge listened to the explanation.
* Dependent clause: in order that he might decide fairly
The bolded phrase "in order that he might decide fairly" tells us the purpose of the judge listening to the explanation. It is a dependent clause, meaning it cannot stand alone as a sentence. The subordinating conjunction "in order that" connects the dependent clause to the independent clause, making it a complete sentence.