NICAEA AND THE HOLY SPIRIT
"AT THIS point you might ask: 'If the Trinity is not a Biblical teaching, how did it become a doctrine of Christendom?' Many think that it was formulated at the Council of Nicaea in 325 C.E.
That is not totally correct, however. The Council of Nicaea did assert that Christ was of the same substance as God, which laid the groundwork for later Trinitarian theology. But it did not establish the Trinity, for at that council there was no mention of the holy spirit as the third person of a triune Godhead."
Much could be said in refutation of this short introduction alone; remember, the Church Fathers leading up to Nicaea had already been teaching for over two centuries that "Christ was of the same substance as God." What is important about this introduction, however, is the impression given that the Council did not teach that the Holy Spirit is one of the Persons in the Trinity.