A few quotes from the Rabbi on 'Israel and the Nations'
in which he teaches that it is obligatory to attend the funeral of a deceased Gentile, even the lesser ones among them.
His Honor also asked whether it is permissible to attend a Gentile's funeral. My friend! This matter is an obligation, to maintain amity, even with the lesser ones among them, and certainly if he is among his followers, for they have a share in the World to Come.
Otzar HaMichtavim, Chapter 1, letter 240, p. 108. Published by Otzrot HaMaghreb, Bnei Issachar Institute, Jerusalem, 1998
