The rationale for the changes in the laws of Torah in Reform Judaism can be found by consulting 'REFORM JUDAISM FROM THE POINT OF VIEW OF THE REFORM JEW' in Jewish Encyclopedia (online), where it is stated: 'The Law, often of non-Jewish origin, is the product of time, and is subject to growth and change in the course of time. . . . The laws regulating marriage and divorce, as developed more especially in Talmudic casuistry, often operate unjustly (see Get) and are, in view of the better provisions in the civil codes of modern nations, amended and in many respects superseded by the law of the land (see Monogamy). Woman is no longer deemed to be a minor, but is admitted to full participation in the religious life of the congregation.' This is essentially the thought expressed in the Chumash of Reform Judaism The Torah: A Modern Commentary (2005) edited by Rabbi Gunther Plaut.
For the changes in Conservative Judaism, see Etz Hayim: Torah and Commentary (2004).
For Orthodox Judaism, Rabbi Jonathan Sacks, former Chief Rabbi of England, in Crisis and Covenant: Jewish Thought After the Holocaust, states:
God’s Law is Unchanging, but Its Application Does Change
Torah does not change. But in one sense, halakhah does change. For halakhah is the application of Torah to specific circumstance, and circumstances change. What then are the parameters within which the law is given to adjustment? This is Maimonides’ classic formulation:
"God knew that the judgements of the Law will always require an extension in some cases and curtailment in others, according to place, event and circumstance. He therefore forbade adding to or subtracting from the Law … but at the same time gave permission to the sages–the Great Sanhedrin–of every generation to make fences around the judgements of the Law for their protection … and similarly they have the power temporarily to dispense with some religious act prescribed in the Law or to allow that which is forbidden if exceptional events and circumstances require it … By this method the Law will remain permanently the same but yet will admit at all times and under all circumstances of such temporary modifications as are indispensable."
So halakhah can and does change, but always to preserve the essential integrity of biblical law. We should note however that Maimonides makes a distinction that substantially tilts the balance of halakhah in the direction of conservatism. A protective decree or enactment created by the sages–a "fence around the law"–is permanent, whereas a suspension of the law is always only temporary." Rabbinic law, that is to say, has an inbuilt bias toward greater stringency over time.
Who May Authorize Changes in the Application of Halakhah?
This is compounded by the issue of juridical authority, hinted at in Maimonides’ reference to the Great Sanhedrin. This supreme court had considerable powers to create new law. But as its jurisdiction grew more circumscribed under Roman rule and as the center of Jewish life shifted to Babylon, Jewry was left without a central authority.
According to Maimonides, after the closure of the Babylonian Talmud no one had the power to legislate for all Israel. At most, a court was able to issue rulings for its own immediate locality, although some post-talmudic rulings gained widespread acceptance. The power to create new law had lapsed. The rebirth of the state of Israel led some thinkers, most notably Rabbi Judah Leib Maimon, to advocate the reconstitution of the Sanhedrin. But this would have required broad support among Israel’s religious leaders, and it was not forthcoming.
We would be wrong to conclude that there is no scope for development in Jewish law. For what cannot be achieved through legislation can sometimes be achieved through interpretation. A new problem is rarely so exactly like others in the past that precedent dictates an unequivocal answer to a halakhic query. Since there are differences in the details and circumstances, it can be argued that the extant rules do not apply to the present case. Halakhic authorities are constantly called upon to adjudicate new questions and, as we will see in due course, there have been areas in which significant changes have occurred in Jewish law in the twentieth century.
Change in Jewish Law is a Reality, Not a Value
But it would certainly be wrong to see change as a value in Jewish law. To the contrary, the central underlying proposition of the halakhah is that it articulates, within the limits of human understanding, the will of God as set forth in the Torah. Rabbinic tradition sees all valid Jewish law as inherent in the original revelation at Sinai. It is uncovered rather than made. Neither a prophet nor a sage has the authority to alter the terms of the covenant.
The rabbis were emphatic in seeing their interpretations and decisions as strictly continuous with biblical precedent. As the third-century teacher Rabbi Joshua ben Levi put it, "Bible, Mishnah, Talmud and [Aggadah], even what a senior disciple is due to teach in the presence of his master, were already stated to Moses at Sinai." Procedurally, therefore, any new ruling must be rendered consistent with the antecedent sources. Any departure from precedent must be temporary, justified by emergency conditions and undertaken with the express purpose of safeguarding Jewish law as a whole.
Developments within the halakhic system are thus homeostatic rather than evolutionary. They are undertaken to restore equilibrium rather than to transform. Halakhah is the application of an unchanging Torah to a changing world. Halakhah changes so that the Torah should not change. (See 'Orthodox Judaism and Halakhah' - My Jewish Learning.com