1 sn No object is supplied for the verb love (the author with his propensity for obscurity has left it to the readers to supply the object). The obvious objects that could be supplied from the context are either God himself or other believers (the brethren). It may well be that the author has both in mind at this point; the statement is general enough to cover both alternatives, although the following verse puts more emphasis on love for the brethren.
2 tn Grk “if anyone should say…”
3 tn “Yet” is supplied to bring out the contrast.
6 sn In 4:20 the author again describes the opponents, who claim to love God. Their failure to show love for their fellow Christians proves their claim to know God to be false: The one who does not love his fellow Christian whom he has seen cannot love God whom he has not seen.