{Is come} (h(886b)ei). Present active indicative, but the root
has a perfect sense, "has come." See ex(886c)thon kai h(886b)(935c) in  Joh
8:42 . {An understanding} (dianoian). Here alone in John's
writings, but in Paul ( Eph 4:18 ) and Peter ( 1Pe 1:13 ). John
does not use gn(9373)is (knowledge) and 
ous (mind) only in  Re
13:18  17:9 . {That we know} (hina gin(9373)komen). Result clause
with hina and the present active indicative, as is common with
hina and the future indicative ( Joh 7:3 ). It is possible that
here o was pronounced (935c) as a subjunctive, but many old MSS.
have hina gin(9373)kousin (plainly indicative) in  Joh 17:3 , and
in many other places in the N.T. the present indicative with
hina occurs as a variant reading as in  Joh 5:20 . {Him that is
true} (	on al(8874)hinon). That is, God. Cf.  1:8 . {In him that is
true} (en t(9369) al(8874)hin(9369)). In God in contrast with the world "in
the evil one" (verse  19 ). See  Joh 17:3 . {Even in his Son
Jesus Christ} (en t(9369) hui(9369) autou I(8873)ou Christ(9369)). The autou
refers clearly to en t(9369) al(8874)hin(9369) (God). Hence this clause is
not in apposition with the preceding, but an explanation as to
how we are "in the True One" by being "in his Son Jesus Christ."
{This} (houtos). Grammatically houtos may refer to Jesus
Christ or to "the True One." It is a bit tautological to refer it
to God, but that is probably correct, God in Christ, at any rate.
God is eternal life ( Joh 5:26 ) and he gives it to us through
Christ.