I am reading Chapter 10 of Harry Potter and the Deathly Hallows, and I don't understand this part:
“that Regulus changed his mind . . . but he doesn’t seem to have explained that to Kreacher, does he? And I think I know why. Kreacher and Regulus’s family were all safer if they kept to the old pure-blood line. Regulus was trying to protect them all.”
What did Regulus's situation have to do with the old pureblood line? How was Regulus trying to protect his family by stealing the Horcrux?