When your child asks you at some point in the future,
saying, “What are the testimonies, rules, and ordinances
that G-d, our G-d, has commanded you?”
Deuteronomy 6:20
The Torah’s “ordinances” are the commandments that human reason would dictate on its own, such as the prohibitions against thievery, murder, and so on. “Testimonies” are the commemorative commandments, such as the holidays, tefillin, and so on, which mortal intellect would not otherwise legislate but which make perfect sense once the Torah commands them. “Rules” refer to the commandments that have no rational basis (even if some lesson can be inferred from them), such as the prohibitions of mixing milk and meat, mixing wool and linen, or the rite of purification with the ashes of the red cow.
Although every commandment in the Torah falls into one of these three categories, we are bidden to fulfill every commandment in all three ways: Every commandment challenges us to understand its message to us, and in that sense is an “ordinance.” Similarly, every commandment is an expression of G-d’s inscrutable will, despite the fact that we can grasp some elements of its meaning, and in that sense is a “rule.” Finally, every commandment testifies to our relationship with G-d, and is thus a “testimony."
--Daily Wisdom Volume 3