I believe the word "God" is often used as a collective noun, like "team," "partnership," "jury" and "committee." The individuals who make up each of these entities are unique. They are physically distinct from one another. My husband and I are a "couple." Notice the use of the singular indefinite pronoun "a." Since it is singular, the word which follows (i.e. "couple") is singular. But since it is a collective noun, we know that it has to be referring to more than one individual. If either my husband or I were not a part of this union, we could not be spoken of as a "couple." The "couple" would simply cease to exist. As united as we may be in many ways, when he is out on the golf course and I am at home feeling sorry for myself because I am a golf widow, we are definitely two physically distinct beings. In this way, we can be divided but still be a couple.
The word "God" is also used as a title. It can be applied to all three of the members of the Godhead, who are "one God," but it can also be applied to each one individually. Normally, I use the word "God" to refer to God the Father, even though I believe the Son to be every bit as divine as I believe the Father to be. When I say I worship "God," I worship God as one "Godhead," because they are so perfectly united in will, purpose, mind and heart, that I could not conceivably worship one without worshipping the others.
To me, the more problematic word is "substance." It just sets off all kinds of red flags in my mind. What is a "substance." When Jesus walked the earth, he definitely had a physical form (which I believe He still has), the substance of which was flesh, bone, etc. You believe, I'm quite certain, that His Father has no form, that His substance is incorporeal and invisible. How then can it be said that they are part of the same substance?
In the terms of form and substance:
Jesus' body was his form.
His substance, or essence, was both human and divine.
God the Father has no form.
His substance, or essence, is divine.
You would have to famaliarize yourself with the terms used in the heretical arguments of the time to understand the necessity of formulaic creeds.
And what's wrong with the way the Bible explains their relationship with each other? Why are the creeds needed if they do not merely re-state what the Bible says?
There were no printing presses when the creeds were formulated. Believers did not have copies of the Bible to consult. And because centuries ago, the creeds cleared away the heresies regarding the nature of Jesus, those heretical arguments are no longer a part of western culture. The creeds did their job.