If God so loved us (ei houtōs ho theos ēgapēsen hēmas). Condition of first class with ei and the first aorist active indicative. As in Joh 3:16, so here houtōs emphasises the manifestation of God’s love both in its manner and in its extent (Rom 8:32).
Ought (opheilomen). As in 1Jo 2:6. Noblesse oblige. “Keep on loving,” (agapāin) as in 1Jo 3:11.