shabbat clothes and messiah’s coming

This acclaimed commentary concludes this section with a fascinating comment: In this light one may understand an oral tradition passed down from the Vilna Gaon (see Chevlei Mashaiach BiZemaneinu, p. 134), that when the Russian navy passes through the Bosporus it will be time to put on Sabbath clothes (in anticipation of the coming Mashiach.) what does this passage mean? and what are sabbath clothes and of what significance are these clothes in general and in light of messiah’s coming? shalom

My understanding is that Gedolim in each generation viewed certain occurrences which were unthought of as having influence on the coming of the Mashiach or the coming of the "Ketz" or as a "ketz"on its own to a certain degree. The significance of wearing Shabbat clothes would be out of respect for the Mashiach who is expected to come and actually wearing them means that the person is in true anticipation of Mashiach's coming.