The 1837 edition increased the parallelism of the text by inserting your before Savior; perhaps the change was consciously made, although Joseph Smith did not mark the change in the printer’s manuscript. Elsewhere in the text there are two occurrences of “our Lord and Savior”:
But there are no cases for which the determiner occurring with Lord is repeated before a following conjunct. These two examples of “our Lord and Savior” suggest that the 1837 change in 2 Nephi 31:13 does not represent systematic editing. The earliest reading in 2 Nephi 31:13, without the repeated your, probably represents the original text. For additional discussion, see conjunctive repetition in volume 3.
Summary: Restore in 2 Nephi 31:13 the reading of the earliest text, without the repeated your in “your Lord and Savior”; this reading is consistent with the two occurrences of “our Lord and Savior” in the Book of Mormon.