{Hereby} (en tout(9369)). John's usual phrase for the test of
the sincerity of our love. "The love of God and the love of the
brethren do in fact include each the other" (Westcott). Each is a
test of the other. So put  3:14  with  5:2 . {When} (hotan).
"Whenever" indefinite temporal clause with hotan and the
present active subjunctive (the same form agap(936d)en as the
indicative with hoti (that) just before, "whenever we keep on
loving God." {And do} (kai poi(936d)en) "and whenever we keep on
doing (present active subjunctive of poie(935c)) his commandments."
See  1:6  for "doing the truth."