17 The name Father has thus been revealed to men; the question arises, What is this Father's own name? Yet surely the name of God has never been unknown. Moses heard it from the bush, Genesis announces it at the beginning of the history of creation, the Law has proclaimed and the prophets extolled it, the history of the world has made mankind familiar with it; the very heathen have worshipped it under a veil of falsehood. Men have never been left in ignorance of the name of God.
And yet they were, in very truth, in ignorance. For no man knows God unless He confess Him as Father, Father of the Only-begotten Son, and confess also the Son a Son by no partition or extension or procession, but born of Him, as Son of Father, ineffably and incomprehensibly, and retaining the fullness of that Godhead from which and in which He was born as true and infinite and perfect God. This is what the fullness of the Godhead means. If any of these things be lacking, there will not be that fullness which was pleased to dwell in Him. This is the message of the Son, His revelation to men in their ignorance. The Father is glorified through the Son when men recognise that He is Father of a Son so Divine.
Source: On the Trinity (New Advent)