Walaikum salam wrt,
All praise be to Allah.
I am happy to answer your questions according to the view of the Ulema (Islamic scholars). If one listens to the Ulema, they will be following right guidance, and they will achieve true happiness in both this world and the next. This following and listening has to come from an attentive heart, ie. there has to be love for the Prophet, may Allah's blessings and peace be upon him, and his inheritors, ie. the rightly guided Ulema. Without love for Allah, and His Messenger, may Allah's peace be upon him, all manner of logic and reasoning are useless. We love Allah more when we realize His love for us, the bounties He bestows on us, when we relect on the blessings that we have.
1.) The guiding principle in Islam is that one should choose a spouse based on piety and religiousness. Allah says in Surah Baqarah verse 221v (translation of meaning):
"And do not marry the disbelieving women until they believe."
Likewise, the Prophet, may Allah's blessings and peace be upon him, said:
"Choose the religious (wife), may you be successful!"
However, Allah Most High also says, in verse 5 of Surah Ma'ida :
"Permissable for you is the food of the People of the Book, and your food is permissable for them, (and permissable in marriage are) the chaste women from the believers, and also chaste women from the People of the Book before your time..."
2.) A small minority of scholars ruled by the first verse alone and stated that it is forbidden to marry women of the People of the Book, and this was the opinion of the great Sahabi Ibn Umar. He said, "What shirk can be greater than saying "Jesus is my Lord?"
However, the majority of scholars, and the four Imams, stated that it is permissable to marry Christian and Jewish women, with certain conditions.
What is the wisdom in Allah Most High allowing a Muslim to marry a Christian or Jewish woman? The scholars have stated that in allowing such marriages, the expectation is that the woman would eventually accept Islam, though as you correctly stated, she cannot be forced to do so. This is a testament to Islam's concillatory approach to the People of the Book, and a means of dawah for them, that by the grace of Allah, has led to the guidance of many to the path of truth.
3.) You say that Judaism and Christianity were not as far away from the truth in the time of the Prophet, may Allah's peace and blessings be upon him, as they are today. I have not heard this statement from any of the scholars, but I have often heard it repeated by people. You need to provide proof for this. It is stated in the Quran that the Jews said, "Uzair is the son of Allah.", and that the Christians said, "God has taken a son." SubhanAllah! This misguidance in Christianity came about long before Islam, during the time of Saul of Tartus, who later became known as Paul the 'apostle'. To say that Christians and Jews today are not as 'practicing' is not really relevent, since their misguidance is in Aqeedah, ie. beliefs more than it is in actions.
However, if a woman apostates, for example she becomes an atheist, or reverts from Islam to Christianity, she becomes forbidden to marry. This is agreed upon by the scholars. We have to stay Muslims, and hold on the faith. This is the only way to success.
Finally, your note about chastity being required for both men and women is well taken, and Allah Most High mentions both men and women when speaking of lowering the gaze in Surah Nur. However, Islam emphasizes chastity on the part of a Christian or Jewish woman in particular since their religions do not place an emphasis on hijab, khalwa, and hayaa', and because of the good opinion and respect Islam affords Muslim women in this regard. Furthermore, since a woman's charms may be a temptation to men, she is expected to be chaste in appearance and cover properly to protect society from fitna, and to protect her from being molested. Likewise, a man is expected to lower his gaze and protect his private parts.
Indeed, Islam remains the only religion on earth that holds human society to such high standards.
The Ulema say that it is inappropriate for a wife to stay with an adulterous husband, though it may be culture that encourages her to do so. In this case, one should follow Islam, and get out of the relationship through the appropriate Islamic means.
And Allah knows best.
PS. Here is a relevant post regarding the correct conditions for marriage:
Praise be to Allaah.
Firstly, for a marriage to be valid in the Islam, the following conditions must be fulfilled:
1. the proposal of your guardian – who may be your father or whoever is acting in his place if he is not there, on the condition that he is of the same religion as you – by his saying, for example, “I offer my daughter in marriage to you.”
2. Acceptance on the part of the husband by saying, for example, “I accept.”
3. The contract was done in the presence of two Muslim witnesses
– then the marriage is valid. If any of these conditions is missing, then the marriage is not valid, and you have to do it again. The place where the marriage contract is done does not have any effect on the validity of the marriage.
Secondly: this question caught our attention because of your keen interest in finding out the rules of the Islamic religion concerning this matter. Perhaps this will lead you to enquire about greater realities, the most important of which is, which is the true religion?
Permit us to ask you the following questions:
Do you want a happy life? Do you care about finding contentment? Are you looking for the truth? Do you want a good and righteous life for your children?
If you do, then please – may Allaah guide you and us to the truth – consider the following:
That Allaah has created mankind for a great purpose, which is to worship Allaah alone with no partner or associate. Allaah says (interpretation of the meaning):
“And I (Allaah) created not the jinn and mankind except that they should worship Me (Alone).
I seek not any provision from them (i.e. provision for themselves or for My creatures) nor do I ask that they should feed Me (i.e. feed themselves or My creatures).
Verily, Allaah is the All-Provider, Owner of Power, the Most Strong”
Allaah sent the Messengers to call mankind to this purpose. He said (interpretation of the meaning):
“And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): “Worship Allaah (Alone), and avoid (or keep away from) Taaghoot (all false deities, i.e. do not worship Taaghoot besides Allaah).” Then of them were some whom Allaah guided and of them were some upon whom the straying was justified. So travel through the land and see what was the end of those who denied (the truth)”
Then Allaah sent the final Messenger, Muhammad (peace and blessings of Allaah be upon him). He was the last of the Prophets and Messengers. Allaah says (interpretation of the meaning):
“Muhammad is not the father of any of your men, but he is the Messenger of Allaah and the last (end) of the Prophets. And Allaah is Ever All-Aware of everything”
“Muhammad is the Messenger of Allaah. And those who are with him are severe against disbelievers, and merciful among themselves. You see them bowing and falling down prostrate (in prayer), seeking Bounty from Allaah and (His) Good Pleasure. The mark of them (i.e. of their Faith) is on their faces (foreheads) from the traces of prostration (during prayers). This is their description in the Tawraat (Torah). But their description in the Injeel (Gospel) is like a (sown) seed which sends forth its shoot, then makes it strong, and becomes thick and it stands straight on its stem, delighting the sowers, that He may enrage the disbelievers with them. Allaah has promised those among them who believe (i.e. all those who follow Islamic Monotheism, the religion of Prophet Muhammad till the Day of Resurrection) and do righteous good deeds, forgiveness and a mighty reward (i.e. Paradise)”
One of the reasons why He sent the Messengers was so as to establish proof against mankind, lest they say, “No Messenger came to us and no one told us that Allaah commanded us to worship Him.” Allaah says (interpretation of the meaning):
“Verily, We have sent the Revelation to you (O Muhammad) as We sent the Revelation to Nooh (Noah) and the Prophets after him; We (also) sent the Revelation to Ibraaheem (Abraham), Ismaa‘eel (Ishmael), Ishaaq (Isaac), Ya‘qoob (Jacob), and Al-Asbaat [the offspring of the twelve sons of Ya‘qaab (Jacob)], ‘Eesa (Jesus), Ayyoob (Job), Yoonus (Jonah), Haaroon (Aaron), and Sulaymaan (Solomon); and to Daawood (David) We gave the Zaboor (Psalms).
And Messengers We have mentioned to you before, and Messengers We have not mentioned to you, — and to Moosa (Moses) Allaah spoke directly.
Messengers as bearers of good news as well as of warning in order that mankind should have no plea against Allaah after the (coming of) Messengers. And Allaah is Ever All-Powerful, All-Wise
We call you, and everyone who does not follow the religion of Islam, to hasten to obey the command of Allaah by believing in Him alone, with no partner or associate, and to believe in His Prophet Muhammad (peace and blessings of Allaah be upon him), whom Allaah sent to all of creation, men and jinn alike. Allaah has commanded them to do this, as He says (interpretation of the meaning):
“O mankind! Verily, there has come to you the Messenger (Muhammad) with the truth from your Lord. So believe in him, it is better for you. But if you disbelieve, then certainly to Allaah belongs all that is in the heavens and the earth. And Allaah is Ever All-Knowing, All-Wise.
O people of the Scripture (Christians)! Do not exceed the limits in your religion, nor say of Allaah aught but the truth. The Messiah ‘Eesa (Jesus), son of Maryam (Mary), was (no more than) a Messenger of Allaah and His Word, (“Be!” — and he was) which He bestowed on Maryam (Mary) and a spirit (Rooh) created by Him; so believe in Allaah and His Messengers. Say not: “Three (trinity)!” Cease! (it is) better for you. For Allaah is (the only) One Ilaah (God), glory is to Him (Far Exalted is He) above having a son. To Him belongs all that is in the heavens and all that is in the earth. And Allaah is All-Sufficient as a Disposer of affairs”
Allaah has told us in His Noble Book (the Qur’aan) that He does not accept any religion other than Islam. Allaah says (interpretation of the meanings):
“And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers”
[Aal ‘Imraan 3:85]
“Allaah bears witness that Laa ilaaha illa Huwa (none has the right to be worshipped but He), and the angels, and those having knowledge (also give this witness); (He always) maintains His creation in justice. Laa ilaaha illa Huwa (none has the right to be worshipped but He), the All-Mighty, the All-Wise.
Truly, the religion with Allaah is Islam. Those who were given the Scripture (Jews and Christians) did not differ except, out of mutual jealousy, after knowledge had come to them. And whoever disbelieves in the Ayaat (proofs, evidences, verses, signs, revelations, etc.) of Allaah, then surely, Allaah is Swift in calling to account
[Aal ‘Imraan 3:18-19]
Do not forget that if you become Muslim, it will be better for your children, so that they will not be confused or suffer from mental anguish, and say, “Our father is a Muslim and our mother is a Christian, so who should we follow?”
Perhaps thinking through these matters more deeply will lead to a good result, by Allaah’s leave. Strive to read a sound translation of the Qur’aan, which is considered to be the miracle of the Prophet of Islam, then read the biography of the Messenger Muhammad (peace and blessings of Allaah be upon him), and how Allaah granted success to him and his Companions, and how Allaah supported him with miracles, such as making water flow from between his fingers and the splitting the moon, when the mushrikoon (polytheists) asked for a sign – so he commanded the moon to split, and it split in two – and other events which are recorded in his Seerah (biography). And he also spoke of unseen matters which could not be known except by means of Revelation, such as when he said that the empires of the Persians and Romans (Byzantines) would be conquered before it happened, and other matters which are indicative of his Prophethood. We ask Allaah to guide us all.
Sheikh Muhammed Salih Al-Munajjid