{That Jesus is the Christ} (hoti I(8873)ous estin ho Christos).
The Cerinthian antichrist denies the identity of Jesus and Christ
( 2:22 ). Hence John insists on this form of faith (pisteu(936e)
here in the full sense, stronger than in  3:23  4:16 , seen also
in pistis in verse  4 , where English and Latin fall down in
having to use another word for the verb) as he does in verse  5 
and in accord with the purpose of John's Gospel ( 20:31 ).
Nothing less will satisfy John, not merely intellectual
conviction, but full surrender to Jesus Christ as Lord and
Saviour. "The Divine Begetting is the antecedent, not the
consequent of the believing" (Law). For "is begotten of God" (ek
tou theou gegenn(8874)ai) see  2:29  3:9  4:7  5:4,18 . John appeals
here to family relationship and family love. {Him that begat}
(	on genn(8873)anta). First aorist active articular participle of
genna(935c), to beget, the Father (our heavenly Father). {Him also
that is begotten of him} (	on gegenn(886d)enon ex autou). Perfect
passive articular participle of genna(935c), the brother or sister
by the same father. So then we prove our love for the common
Father by our conduct towards our brothers and sisters in Christ.