Church history says that the Trinity is the true doctrine of what the earliest christians believed in.
http://www.newadvent.org/cathen/15047a.htm
The controversy with the Sabellians in the third century
proves conclusively that she would tolerate no deviation from Trinitarian
doctrine. Noetus of Smyrna, the originator of the
error, was condemned by a local
synod, about A.D. 200. Sabellius, who propagated the same
heresy at
Rome c. A.D. 220, was
excommunicated by
St. Callistus. It is
notorious that the
sect made no appeal to
tradition: it found Trinitarianism in possession wherever it appeared — at
Smyrna, at
Rome, in
Africa, in
Egypt. On the other hand,
St. Hippolytus, who combats it in the
"Contra Noetum", claims
Apostolic tradition for the
doctrine of the
Catholic Church: "Let us
believe, beloved brethren, in accordance with the
tradition of the
Apostles, that
God the Word came down from
heaven to the
holy Virgin Mary to
save man."
The
witness of the
doxologies is no less striking. The form now universal, "
Glory be to the Father, and to the
Son, and to the
Holy Ghost," so clearly expresses the Trinitarian
dogma that the
Arians found it
necessary to deny that it had been in use previous to the
time of Flavian of Antioch (Philostorgius, "Hist. eccl.", III, xiii).
It is
true that up to the period of the
Arian controversy another form, "
Glory to the Father, through the
Son, in the
Holy Spirit," had been more common (cf.
Clement's Epistle to the Corinthians 58-59;
Justin,
First Apology 67). This latter form is indeed perfectly consistent with Trinitarian
belief: it, however, expresses not the coequality of the Three
Persons, but their operation in regard to
man. We live in the
Spirit, and through Him we are made partakers in
Christ (
Galatians 5:25;
Romans 8:9); and it is through
Christ, as His members, that we are worthy to offer praise to
God (
Hebrews 13:15).
But there are many passages in the ante-Nicene Fathers which show that the form, "
Glory be to the Father and to the
Son, and to [with] the
Holy Spirit," was also in use.
.