A brief explanation at the outset may help the reader to follow more
intelligently the history of Unitarianism. As is well known, the chief
issue between Trinitarians and Unitarians arises in connection with the
relation of Jesus Christ to God, questions concerning the Holy Spirit
being usually less discussed. There are consequential issues also,
bearing upon man's nature, atonement, salvation, and other subjects, but
these call for no remark here. In its full statement, as given for
instance in the 'Athanasian Creed,' the Trinitarian dogma presents the
conception of Three 'Persons' in One God--Father, Son, and Holy
Spirit--'Persons' with different: functions, but all equal and
co-eternal. The Eastern (Greek Orthodox) Church differs from the Western
(Roman Catholic) in holding that the Third Person 'proceeds' from the
Father alone; the Western adds--'and from the Son' (_filioque_). The
full dogma as given in the 'Athanasian Creed' is not thought to be
earlier than the fifth century; debates as to the 'two natures' in
Christ, and the 'two wills,' and other abstruse points involved in the
dogma, continued for centuries still. At an earlier period discussion
was carried on as to whether the Son were of the 'same substance'
(_homo-ousion_) or 'similar substance' (_homoi-ousion_) with the Father.
The latter view was held by Arius and his party at the Council of
Nicaea, A.D. 325. Athanasius held the former view, which in time, but
only after many years of controversial strife and actual warfare, became
established as orthodox. The Arians regarded the Son, as a subordinate
being, though still divine. Another variety of opinion was put forth by
Sabellius (_c._ 250 A.D.), who took the different Persons to be so many
diverse modes or manifestations of the One God. This Sabellian idea,
though officially condemned, has been often held in later times.
Socinianism, so far as regards the personality and rank of Christ,
differed from Arianism, which maintained his pre-existence, though not
eternal; the Socinian doctrine being that the man Jesus was raised by
God's approving benignity to 'divine' rank, and that he thus became a
fit object of Christian 'worship.' The Humanitarian view, finally,
presented Jesus as a 'mere man,' i.e. a being not essentially different
in his nature from the rest of humankind. Modern Unitarianism, however,
usually avoids this kind of phrase; 'all minds,' said Channing, 'are of
one family.'