I commend to you the Athenasian Creed for an accurate summary of this doctrine.
English speaking churches often replace the word "catholic," which means "universal" with the word "Christian" in the Nicene Creed. In this creed, however, the word has been retained for 500 years.
Whosoever will be saved,
before all things it is necessary
that he hold the catholic faith;
Which faith except every one do keep
whole and undefiled,
without doubt he shall perish everlastingly.
And the catholic faith is this:
That we worship one God in Trinity,
and Trinity in Unity;
Neither confounding the persons
nor dividing the substance.