God says that He is not a Trinity or any multiple.
Isaiah 45:6
so that from the rising of the sun to the place of its setting people may know there is none besides me. I am Yahwah, and there is no other.
It is unfortunate that people will not even believe God. No other, is no other person. You can not say that if you are a trinity or a multiple.
There is no other
Indeed, and he warns of that in other places in scripture as well.
Deuteronomy 6:4 being one of many
However, let me say that the pronouns God uses in Isaiah 45:6 are clearly referring to a single entity not to multiple persons or beings.
"there is none beside ME"
"I am Yahwah"
As many times as God refers to himself as "I" or "me" in scripture, it is clear that verses like Genesis 1:26 as an exception to be learned to understood in the light of all the places where HE refers to Himself in the singular.. As soon as the next verse, Genesis 1:27, God goes to referring to himself in the singular.
Although trinitarians use that verse to support their theology, they do not show how they get three of that verse or any other specific number.
As often as God uses figures of speech in His word, and here in Genesis 1, it is necessary that we look at Genesis 1:26 as one of those places where God uses a figure of speech to emphasize a truth He is sharing.
Knowing the figure of speech heterosis of number, or as some call it here, the majestic plural or plural of intensity, it is a simple and straightforward conclusion that God is emphasizing the grandness or greatness of what He, not they, are about to do, that is to make man in God's image.
So God created man in HIS own image, in the image of God created HE him, male and female create HE them.
Trinitarians like to use I Thessalonians 5:23 to support their theory, ie, God, being a three part being, God create man a three part being. Interestingly, and more specifically, if the image of God is Father and Son and Holy Spirit, the trinitarians fail to explain how a man or a woman resembles Father, Son and Holy Spirit and why there is no such resemblance, given that man was created in God's image.
Where is the Father, Son and Holy Spirit clearly depicted in Adam and Eve or any of their progeny?
It is clear that of body and soul and spirit, and of Father and Son and Holy Spirit, we have one, but only one image of the other. That is spirit and Holy Spirit. But how will they explain how either the Father or Son is body or how the Father or son is soul? God is spirit, John 4:24, Is body now spirit?
That God is not a trinity is self evident. Granted there are some verses that we have to dig deeper to find how they fit with the hundreds of clear verses, but the work is worth it for God's word does contradict itself.
God is one, if God meant, three in one, He would have said so in genuine scripture.
He means HE, I means I, God is One Lord, not one of three.
God is holy and God is spirit, John 4:23, true worshippers shall worship the Father in spirit and in truth.
Is is the Father who, having called himself by many names in the OT, chooses to be know as the Holy Spirit, also.