The scriptures do not merely assure us that there is one true God. It furnishes us with a description of this one God. Additionally if this one God is the great first cause and is worthy of our confidence in his ability to indefinitely sustain his creation certain things must be through of him that cannot true of any member of Christendom's trinity.
In his book 'the forgotten Trinity' pastor White claims that the one God is 'three whos and one what'. But really it depends on who you ask I've spoken to quite a few trinitarians who insists that the trinity is himself a person. Wouldn't that make him a quadrinity then? The reply some give is that he is not a person in the same way that the constituents of him are because he is also a being. Bit of a fudge if you ask me. But here is the issue the God of the bible is superlative ,as defined by the dictionary.
Psalm83:18ASV "18That they may know that thou alone, whose name is JEHOVAH, Art the Most High over all the earth.,"
Neither the non-being persons nor the personal being nor the impersonal being mentioned in these competing definitions matches this description. They each are matched by others in glory and power. Additionally the bible repeatedly Identifies the Father who by common consent is a single person as the one God of Abraham,Isaac and Jacob who by common consent is a being.
Acts3:13ASV"The God of Abraham, and of Isaac, and of Jacob, the God of our fathers, hath glorified Servant Jesus; whom ye delivered up, and denied before the face of Pilate, when he had determined to release him. "
John8:54ASV"54Jesus answered, If I glorify myself, my glory is nothing: it is my Father that glorifieth me; of whom ye say, that he is your (Lit.the God of you)God;"
Additionally the Father is the God of the Son
John20:17ASV"17Jesus saith to her, Touch me not; for I am not yet ascended unto the Father: but go unto my brethren, and say to them, I ascend unto my Father and your Father, and my God and your God."
Revelation3:12ASV"2He that overcometh, I will make him a pillar in the temple of my God, and he shall go out thence no more: and I will write upon him the name of my God, and the name of the city of my God, the new Jerusalem, which cometh down out of heaven from my God, and mine own new name. " Thus the Father is a person ,a being and the God according to scripture,logic and common sense.
Of course God is necessary ,apart from him none of us would be here and there would be no hope for a perpetual future.
Acts17:28ASV"28for in HIM (Not It)we live, and move, and have our being; as certain even of your own poets have said, For we are also HIS(not its) offspring. " Again this can't be true of any of the members of the trinity or the impersonal/hyperpersonal substance in which they subsists. There are peers who/which are fully God and hence can duplicate/replicate their capabilities. A clear violation of the principle of Occam's razor. Christendom's apologists appeal to this principle as a polemic against polytheism. A polytheist would be justified in arguing that the trinity constitutes a far more egregious violation of this principle than the ancient (or modem) pantheons, these being complementarian and not needlessly redundant like Christendom's trinity.