It's because this sentence is written in the subjunctive form. It's a very formal way of speaking; and is used for talking about opinions, ideas, and possibilities instead of just facts. If this world were just, he would say "everyone receives the honor that is due." But the world is not just, so he's using the subjunctive clause to talk about the ideal situation.
You don't have to use the subjunctive clause in this sentence, it would be equally correct to say
What is just in this social world is that each person receives the honor that is due, given that person's status and position.
The meaning's the same, but because it's not in the subjunctive mood it sounds maybe a little too authoritative. As if he's saying "and that's a fact that everyone agrees with."