{His commandment} (h(8820)entol(8820)autou). {That} (hina).
Subfinal use of hina in apposition with entol(885c) (commandment)
and explanatory of it, as in  Joh 15:12  (entol(8820)hina). See
Christ's summary of the commandments ( Mr 12:28-31  Mt
22:34-40 ). So these two points here (1) {We should believe}
(pisteus(936d)en, first aorist active subjunctive according to B K
L, though Aleph A C read the present subjunctive pisteu(936d)en)
either in a crisis (aorist) or the continuous tenor (present) of
our lives. The "name" of Jesus Christ here stands for all that he
is, "a compressed creed " (Westcott) as in  1:3 . Note dative
onomati here with pisteu(935c) as in  5:10 , though eis onoma
(on the name) in  5:13  Joh 1:12  2:23  3:18 . But (2) we should
love one another" (agap(936d)en all(886c)ous), as he has already urged
( 2:7f.  3:11 ) and as he will repeat ( 4:7,11f.  2Jo 1:5 ) as
Jesus (even as he gave us commandment, that is Christ) had
previously done ( Joh 13:34  15:12,17 ). There are frequent
points of contact between this Epistle and the words of Jesus in
 Joh 13-17 .