To a friend:
I will reply to [your] idea that the tradition is just fashion, changeable, not the same as ‘biblical Judaism’, and not authoritative even if you concede that Christianity is not true.
1. It is promised and also implied a number of times that God will protect His testimony in the mouth of Israel for all generations. This is no ordinary nation or chain of tradition. If you’re looking for the group of Jews whose message is the product of this promise, a good place to start is the community who have a parent-to-child chain of Torah observance through the generations, as designed, and it is traditional Judaism for whom that exists.
2. Numerous laws in the written Torah presuppose unwritten knowledge, and we know that Moshe not only continued to answer practical day-to-day questions for the people, but passed that authority on to the judges and priests. Torah says that ignoring their judgments comes with a death penalty. The Christian hero in the gospels also identified the Pharisees as being in Moshe’s seat, referring to that commandment to listen to them (even though he called them ‘hypocrites’). The rulings of the Sanhedrin are preserved in the rulings and discussions of the Mishnah and Gemarah, and they are incumbent on every Jew to follow…even in the modern situation, until a future Sanhedrin is established. You just CAN’T keep it unless you keep to the Talmud and the living testimonial people.
3. Some of these are original Torah, the living understanding of what the written mitzvot look like in practice. Some are fences for the Torah, to help people truly honour its form. And some are rulings to help the community to embody the spirit of the law.
4. Every stringency comes with a cost, so it has to be for a reason.
5. There are also various customs in place to keep communities, and/or the wider community, practicing together as a single testimonial people. Remember that these people are so scattered and that things become complex in many ‘simple’ areas of Torah when in exile (for example, kashrut). Remember that the law is full of observances, which are alive in actual practice. Customs hold a lot of significance from the heart of many generations!
6. There are legitimate debates in halacha and that is a healthy thing. But once you find a rabbi whose heart and knowledge you trust, ‘ask your rabbi’ is a fair thing to do because the common person needs to be able to live Torah with simplicity. Sometimes there are also extra fences just for simplicity. Today’s context is complicated, and deep discussion happens about how different parts of the Torah (considered even more seriously than rabbinic rulings) may be kept together. It is not a free for all.
7. You were right that not all the mitzvot can be kept right now, but the Torah explicitly tells people to return to the commandments Moshe gave them when in exile. What does that mean? You do what you are able to in each generation, with a heart of obedience and not of speculation. It is scripturally enough.
8. If you want to question any particular law, ruling, or custom, say what it is specifically and I can tell you what it is or why it’s necessary.
9. This is also all only the approach required of Jews in their unique situation. For non-Jews, following morality and loving God are more individual and less ritual, so tend to be more intuitive. Jews have that as well, but also the law… which is life to them, though it is a yoke.
10. Here is what is prayed each day, with love… “Hear, O Israel: The Lord is our God, the Lord alone. You shall love the Lord your God with all your heart, and with all your soul, and with all your might. Keep these words that I am commanding you today in your heart. Recite them to your children and talk about them when you are at home and when you are away, when you lie down and when you rise. Bind them as a sign on your hand, fix them as an emblem on your forehead, and write them on the doorposts of your house and on your gates…” The Torah is a connection with Hashem that Jews have uniquely with Him, and studying and keeping it is a way of knowing Him.