I'm not familiar with the exact term "passive belonging," but it suggests the roles played by some characters in the play. Those characters who did not actively promote the trials, or actively oppose them, would be passive participants in the tragedy as it unfolded. By not objecting, they became participants but in a passive way. They were no less guilty. Herrick might be considered an example. He played his role in coming for Elizabeth. He took no satisfaction in chaining her, but he did not take a moral stand against it. Through his passive attitude, he then became a part of the forces of ignorance and injustice that swept through Salem.