In the Heaven thread, someone actually suggested this. If anyone has any questions about Jews & Judaism, I'll try to answer. I'm neither the most brilliant nor the most foolish Jew in the world. I like to think I'm reasonably well informed. If I can't answer your question, I'll tell you that too. So, fire ahead. If nobody does, that won't offend me either. This is just an offer.
I have two questions, if you don't mind.
As a Christian, I DO NOT believe in the trinity doctrine, since they say there are three persons as God, while YHWH himself has said the he is the only one (as God). And even Jesus said that God is only one (Mark. 12:29)...
The Christian pastors say all over the world that the word "Elohim" is a proof of that God is three persons since it is a plural form. Is it true that all nouns, verbs and adjectives connected with the word "Elohim" in the Tanakh is ALWAYS in a singular form when God is talking about himself?
"Elohim" is a grammatically plural noun, it is true. However, the Rabbis have always understood it to mean that God is speaking in terms of the Royal We, as when Queen Elizabeth says something to the affect of "We are pleased with your report." She certainly is not suggesting that there is more than one of her. Accordingly, so it is with G-d.
And if this is the case, do you agree that the plural form is no proof at all of that HE is schizophrenic as the Father, Son and the holy spirit?
I certainly do agree, most whole-heartedly.
Now, to be fair, there is a Liberal argument, that I myself do not accept, but I shall present it just so it cannot be said that I haven't presented all sides. Liberal Jews, of which I do not count myself one (I classify myself as a traditional Jew, with Orthodox tendencies), have argued that in the Bible (the Jewish Bible, ie, the TaNaKh), when the authors of the Torah (these are Jews who accept the Four Source Theory E,P,J,D of authorship of the Torah; I do not. I personally believe that Moses wrote the Torah under divine guidance from G-d) use the term "Elohim", G-d is referring to himself and the Angels, or the "Divine Beings" (Angels, basically). But even these Jews don't think that G-d is talking to himself as a Trinity, or some perverse schizophrenic nature of himself.
Allow me to please reiterate that I in NO way share views with the Modernist Jews. I find their views distasteful in the extreme. But even they do not hold the idea that G-d is plural.
G-d is inalterably, unavoidably, absolutely, and positively, One. He can't possibly be anything else. To make him something else is to commit idolatry. Or at least that is the general point of view among Jews. Trinitarian Christians only narrowly avoid being stamped as idolators. They manage to avoid this because we do recognise that to them, Jesus IS G-d, not a different G-d, but G-d. As much as we find the belief unacceptable, because it is the Abrahamic G-d they are talking about, we are not inclined to make them idolators, although they get about as close as you can get to it, without actually doing it. Such a belief should be actively fought against, as it is injurious to the spiritual health of the believer thereof. On the other hand, there are far worse beliefs one could have, I suppose.
I hope that helps.