{One} (hen). Neuter, not masculine (heis). Not one
person (cf. heis in  Ga 3:28 ), but one essence or nature. By
the plural sumus (separate persons) Sabellius is refuted, by
unum Arius. So Bengel rightly argues, though Jesus is not
referring, of course, to either Sabellius or Arius. The Pharisees
had accused Jesus of making himself equal with God as his own
special Father ( Joh 5:18 ). Jesus then admitted and proved this
claim ( 5:19-30 ). Now he states it tersely in this great saying
repeated later ( 17:11, 21 ). Note hen used in  1Co 3:3  of the
oneness in work of the planter and the waterer and in  17:11,23 
of the hoped for unity of Christ's disciples. This crisp
statement is the climax of Christ's claims concerning the
relation between the Father and himself (the Son). They stir the
Pharisees to uncontrollable anger.