Hereby (en toutwi). 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 (otan). "Whenever" indefinite temporal clause with otan and the present active subjunctive (the same form agapwmen as the indicative with oti (that) just before, "whenever we keep on loving God." And do (kai poiwmen) "and whenever we keep on doing (present active subjunctive of poiew) his commandments." See 1:6 for "doing the truth."