In the phrase "Ethics is the eternal social or racial mirror", it is likely that an "x" was mistakenly dropped from the word "eternal," making ethics the external social or racial mirror which reflects internal spiritual and religious developments.
P1127:8, 102:8.4
Ethics is the eternal social or racial mirror
which faithfully reflects the otherwise unobservable progress of internal
spiritual and religious developments. Man has always thought of God in the
terms of the best he knew, his deepest ideas and highest ideals. Even historic
religion has always created its God conceptions out of its highest recognized
values. Every intelligent creature gives the name of God to the best and highest
thing he knows.