Our Gemara on Amud Beis discusses the famous principle:

הַשְׁתָּא בְּהֶמְתָּן שֶׁל צַדִּיקִים אֵין הַקָּדוֹשׁ בָּרוּךְ הוּא מֵבִיא תַּקָּלָה עַל יָדָן, צַדִּיקִים עַצְמָן לֹא כׇּל שֶׁכֵּן

Now consider: If, even through the animals of the righteous, the Holy One, Blessed be He, does not bring about a stumbling block, then through the righteous themselves, all the more so is it not so that He does not bring about stumbling blocks?

Based on this, the Arvei Nachal (Nitzavim 1:7) asks a novel question: How can a sage of a later era derive new prohibitions and laws through derashos, does this not reflect poorly on the earlier generation? In other words, retroactively, the sages of a prior generation will have been violating this newly established principle?

If Torah is mere legalizaties, this would not be a question, since before a law is passed it’s not illegal. The sages of a prior generation could not have violated a law that did not exist. However, since we are talking about Torah, which is God’s will, even if not enacted as law per se, violation of a principle still should represent some degree of stumbling for the righteous. After all, as we discussed in Psychology of the Daf Yevamos 96, the forefathers kept the Torah in some form because they were able to intuit the will of God.

Arvei Nachal explains the Torah itself exists in “remez” form but is not brought out into physical reality until humans choose to interpret it. What I believe he is saying is that the Torah has many potential paths to represent God’s timeless and unchanging will. Though God is unchanging, humans encounter the Torah in a physical changing world, and that is why each generation interprets and applies the truths of the Torah. This is how we can understand the dictum of the Torah is not in Heaven, and that the Sages can even outvote God in their halakhic rulings, as we saw in Gemara Bava Metzi’a (59b). Think of Torah like a quantum wave form, that only collapses into a reality after it is observed by humans.

In modern times, without a Sanhedrin that can enact derashos the range of flexibility in interpretation is more limited but ever present in subtle ways. We discussed the ways in which the Torah is open to interpretation and change in human form in Psychology of the Daf Yevamos 35 and 90, and also quoted a powerful assertion of Rav Kook about how halakha still evolves without a Sanhedrin.