Ki Savo: Are You Proud of Your Sins?

In this week's Torah portion, a word appears twice that has no exact parallel in Scripture: "he'emarta" and "he'emircha" in the verses "G-d has set you apart to be his nation" and "You have set G-d apart to be your L-rd." Rashi says that the only similar word in Scripture is in Psalms where it says "the sinners are proud (yisamru) of their sins." Why does this word describing G-d's special relationship with his people appear in a verse with such a negative connotation? Why did the Berditchiver tell the sinner that he was jealous of his reward in the World to Come? When is it good to be proud of your sins?

Based on Likkutei Sichos vol. 9, pp. 162-174.