بسم الله الرحمن الرحيم
Peace be upon you,
Despite the opinion of some of the people here, the Almighty One, blessed be He, does permit polygamy in the Tanakh. However, He also demonstrates the paradigm of marriage in Genesis, with Adam and Eve. Further, as some posters have rightly pointed out, virtually every instance of polygamy is also met with some level of undesirable consequence. Take, for example, the competing wives Hannah and Peninah, or the rival half-siblings such as Jacob and King Jacob's sons. Further, the very verse that permits polygamy is heavily tainted as though polygamy is not the ideal.
Deuteronomy 21:15 said:
15 If a man has two wives, and he loves one but not the other, and both bear him sons but the firstborn is the son of the wife he does not love,
So, then, why does the Tanakh, particularly the Torah, permit polygamy? The Torah is a book that commands and directs inhabitants of Earth. It deals with life in the real world. Sure there is an ultimate, one ideal for all of mankind to follow; but, this is not realistic when you consider the obstacles presented in our world.
Take, for example, that a famine or plague wipes out most of the male population of a tribe or village. How are they to repopulate without the mechanism of polygamy? An excellent example is that of Rabbi Tarfon and his 300 wives. During his time there was a great famine. Being a Kohen, a Priest, he was continuously receiving the priestly tithes from the community. These Biblically mandated tithes were only for the Kohen and his family to eat - the priestly tithe is not to be shared with anyone else. Rabbi Tarfon married the women of the village so that they and their children might eat of the tithes. Without the green-light on polygamy an entire village faced the very real probability of annihilation. (Jerusalem Talmud, Yevamot 4:12)
On a side note, Rabbi Gershom ended the practice of polygamy with a Rabbinical commandment. (There are loopholes for extenuating circumstances) The majority of the Jewish world no longer practices polygamy under Rabbinical ordinance.
Now, let us consider Jesus' comments:
Matthew 5:27-28 said:
27Ye have heard that it was said by them of old time, Thou shalt not commit adultery:
28But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
Jesus is well known for using hyperbole in His teachings. Further, it is important to note that almost all Rabbis create "fences" around mitzvot (commandments) to cause their students/followers to feel as though they have actually broken the mitzvah (commandment) well before they've gotten anywhere close to committing an actual sin.
Particularly, this is a clear example of Jesus using hyperbole, as well as creating a fence, to warn His followers of the path to adultery. Simply lusting after a married woman is not enough to constitute adultery, but He wants you to feel like it is so you will stop well before you're anywhere near actually going home with her.
Furthermore, it is important to note that it is perfectly appropriate for you to lust after your own wife.
Most respectfully,
S.