This is the mistake the Christains made and Baha'u'llah explains this in detail.
To show how clear it is and what he thinks about those that say this about Him, please read this passage so you can know;
"...Certain ones among you have said: “He it is Who hath laid claim to be God.” By God! This is a gross calumny. I am but a servant of God Who hath believed in Him and in His signs, and in His Prophets and in His angels. My tongue, and My heart, and My inner and My outer being testify that there is no God but Him, that all others have been created by His behest, and been fashioned through the operation of His Will. There is none other God but Him, the Creator, the Raiser from the dead, the Quickener, the Slayer. I am He that telleth abroad the favors with which God hath, through His bounty, favored Me. If this be My transgression, then I am truly the first of the transgressors. I and My kindred are at your mercy. Do ye as ye please, and be not of them that hesitate, that I might return to God My Lord, and reach the place where I can no longer behold your faces....."
Now you have to agree that is clear as day.
Christ also made it clear, so instead of trying to understand what is the relationship, people made Christ God as well.
Muhammad then Baha'ullah have cleared it up for all time.
The Messenger is a perfect unblemished mirror, in that way what we see in them is an unblemished reflection of Gods Attributes, as a reflection is not the unknowable Essence of the all mighty God.
That is also as clear as the noon day sun and is also sound biblical reasoning.