The Apostles' Creed is a great aid in doing that, yet it proved insufficient to demonstrate the relationship between the Father, the Son, and the Holy Spirit. Thus for two centuries, men struggled to understand how God could be one God, and how we could worship the Son and not be said to worship another God.
Monarchianism and Arianism were but two great heresies that developed in an attempt to answer these questions. It was two full centuries before the church was able to articulate this understanding of the doctrine of the Trinity. It was implicit in our worship from the beginning, but we were unable to articulate the understand in human language. The Monarchians affirmed the oneness of God but denied that the Son and the Holy Spirit are real Persons, distinct from the Father which is clearly seen in the Scripture.
The Arians acknowledged the distinctness of the Son (and to an extent the Holy Spirit) from the Father, but they did not acknowledge Him to be fully or equally God. Yet Scripture declares, "Php 2:6 Who, being in the form of God, thought it not robbery to be equal with God:
Php 2:7 But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men:
Php 2:8 And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross.
Php 2:9 Wherefore God also hath highly exalted him, and given him a name which is above every name:
Php 2:10 That at the name of Jesus every knee should bow, of things in heaven, and things in earth, and things under the earth;"
Since the 4th century, trinitarian theology has been an essential part of the Gospel in articulating this understanding.
This language and understanding still fall far short of a complete understanding of Gods otherness. However, it is a very helpful tool for expressing our faith. It is also helpful in keeping us from falling into the errors of the past.
It aids us in the understanding that God did not create out of need, for He has never been alone. He has always existed in this perfection of One in Trinity and Trinity in Unity.
This is important because any other understanding steps outside of Orthodox truth in our attempts of worship. And in our worship, it is our desire to be right. To think rightly and worship rightly.
In our attempts to comprehend God, it is generally easier for us to understand what He is not rather than what He is. His otherness leaves us reaching for that which we cannot comprehend in its fullness. It is safest for us simply to state what we believe concerning the Trinitarian nature of God rather than attempt to explain it.
"Thus the connection of the Father in the Son, and of the Son in the Paraclete, produces three coherent Persons, who are yet distinct One from Another. These Three are one essence, not one Person, as it is said, 'I and the Father are One,' in respect of unity of substance, not singularity of number." ~ Tertullian (155-240 AD)
For a much more in-depth study please see the book by Harold O. J. Brown "Heresies"
May the Grace of God be with each of you,