She is a non-Muslim monotheist and is asking why it is not permissible for a Muslim man to marry her?
Question

                Hello and thank you for receiving my question. As a female looking to marry a Muslim guy, I consider myself Natural and organic ideologically. At this point I've Recognized that there is one god, That controls everything And is The Guardian and creator of everything in existence. As far as other things , That religions preach, (Mostly the monotheistic religions) about prophets angels, etc, I'm not disagreeing or agreeing with it at the moment. But I do know that there is one God only.
 With that being said I know some things about Islam where The Muslim man can marry a Christian or Jew female, BECAUSE THEY ARE 'MONOTHEISTIC' Compared to the other religions.
 So my question is if I'm monotheistic just like the Christian and Jewish woman is, Then I should be able to marry this Muslim man. IF YOUR GOING TO SAY NO, because they're people of the book, what's the difference between me if i don't believe/ recognize the prophets yet, and a Christian women who believes in some prophets and not in others like prophet Muhammad. So why the double standards,(if you say no).
 Thank you again for taking time to read this question and please take into consideration that there isnt any other detailed (muslim/ non muslim marriage) question like this on your website so please take time and thought in answering it. Because as simple as your religion is I'm pretty much at the basic similar level with you, that would consider me to be monotheistic although not Muslim
Praise be to Allah.Firstly:
If you really believe in the one God and Creator, then what is your excuse for not believing in His Messengers?
How can you be a believer in God when you do not worship Him according to any religion?
Do you think that believing is a merely theoretical matter that does not require any deeds or obligations?
Belief in God has two aspects:

believing in His Oneness and perfection;
and worshipping Him, seeking to draw near to Him, obeying Him and complying with His commands. That includes believing in His Books and His Messengers.

So long as God has blessed you with insight and understanding, what is keeping you from becoming Muslim?
Entering Islam and hastening to do so, without wasting a single moment, is more appropriate and more important than simply thinking about the issue of marriage or asking about it.
Not one of us can guarantee that he will live a moment longer, but if he enters the true religion, he will attain the means of eternal happiness and will save himself from the fire.
We invite you to do that and advise you to do it, so hasten and do not delay.
Secondly:
Islam is based on being a true slave or servant of God, for the servant can only hear and obey the command of his lord and master.
Whoever believes in God accepts His rulings, submits and surrenders to them, and strives to put them into practice as much as he can.
One of these rulings is the prohibition on marrying a woman who is not a Muslim or one of the People of the Book (Jewish or Christian).
This ruling is definitive in the religion of Islam, and there is no room for debate concerning it.
God, may He be exalted, says (interpretation of the meaning):
“And your Lord creates what He wills and chooses; not for them was the choice. Exalted is Allah and high above what they associate with Him”
[al-Qasas 28:68]
“It is not for a believing man or a believing woman, when Allah and His Messenger have decided a matter, that they should [thereafter] have any choice about their affair. And whoever disobeys Allah and His Messenger has certainly strayed into clear error”
[al-Ahzaab 33:36].
If a monotheistic Muslim woman believes in God and all His Prophets and Messengers, but she disbelieves in one verse of the Book of God [the Qur’an], may He be exalted, or rejects something that is well known to be part of the religion, then she goes beyond the pale of Islam by doing that, and it is forbidden for a Muslim man to marry her.
It is not only the matter of whether a woman is a monotheist or not. If that were the case, it would not be permissible to marry a Christian woman, because in fact she is a polytheist, not a monotheist.
Rather it is the matter of what God has permitted and what He has forbidden, for He is the one who has the power to command and forbid. He has permitted marriage to a Muslim woman and a kitaabi [i.e., Jewish or Christian] woman, and He has not permitted marriage to any other women, so the individual has no option but to accept that and submit to it.
If a person does not understand this principle on which Islam – and all other religions – is based, namely compliance and obedience, then his monotheism or affirmation of God’s oneness will never be sound, and no good deed will ever be accepted from him, no matter how much he claims to be a believer or a monotheist.
God, may He be exalted, says (interpretation of the meaning):
“But no, by your Lord, they will not [truly] believe until they make you, [O Muhammad], judge concerning that over which they dispute among themselves and then find within themselves no discomfort from what you have judged and submit in [full, willing] submission”
[an-Nisaa’ 4:65].
This does not mean that we cannot understand the wisdom behind many teachings; rather we understand a great deal of that, but we believe and we submit, even if it so happens that we do not understand the wisdom behind a particular teaching.
It may be noted here that God, the All-Knowing and All-Aware, knows that the kitaabi [i.e., Jewish or Christian] woman who believes in God, and believes in His messages in general terms, and believes in the resurrection is, as a result of that, close to Islam, and marrying her will, in most cases, call her and her family to Islam, and encourage her to enter Islam, in contrast to a woman who does not believe in God, or in the Prophets, or in the resurrection.
This may be the wisdom behind it, or it may be that we have not got it right in what we have said about the reason behind this teaching.
But whatever the case, we believe that Allah does not prescribe anything except for a wise purpose, and we do not make following any of His rulings dependent upon knowing the wisdom behind it; rather we comply and submit, and we trust that He, may He be glorified, is the All-Knowing, the Most Wise, the All-Aware.
So you should examine the matter in this light, on the basis of the following straightforward approach:
If there is one God and Creator, then it is He Who has the power to command and prohibit, and He is most merciful and most kind; He sent the Messengers and revealed the Books to guide thereby whoever wants to be His slave and servant.
The one who attains the honour of this servitude to God has no right to object to His rulings.
So you must rectify your belief in God’s oneness and your faith in Him, by believing in His prophets and messengers and entering this great religion which God approves for His slaves and servants, so that you may attain happiness and save yourself from the Fire.
We hope that your common senses and insight will lead you to that very soon, if God wills.
We ask God to open and illuminate your heart, and guide you to that which will lead to your success.
And Allah knows best.