Our Gemara on Amud Beis makes a derivation from the word, “veyassaf - he will add”, that the ⅕ penalty for redeeming a consecrated object applies even to a situation of ⅕ on ⅕. This occurs in a case where a consecrated item is redeemed with another consecrated item (now with an additional ⅕). If this item is to be redeemed, he must now add a ⅕ onto this new item, which is effectively ⅕ on ⅕.

Gilyonei Shas (Yevamos 69a, “zar’o”) explains the linguistic rationale for this derivation. In Hebrew, the word “yassaf” connotes additional onto the principal. Meaning an addition of the same kind. Thus, the ⅕ here in the verse means a new ⅕ added to the prior ⅕.

The Maharal (Gur Aryeh, end of Parashas Shelach) uses this same idea to explain a teaching in Sanhedrin (56b) about the laws that the Jews were taught in Mara (see Shemos 15:25) prior to the giving of the Torah on Mount Sinai. 

The Jewish people were commanded to observe ten mitzvos when they were in Mara: The Seven that the descendants of Noah accepted upon themselves, and God added to them the following mitzvos: Judgment, Shabbos, and honoring one’s father and mother.

Maharal asks, we have learned that the Jews violated their first Shabbos when they gathered the Manna against Moshe’s directions (Shabbos 118b). However, if the Jews were given the laws of Shabbos at Mara, then at least we can say they did not violate their first shabbos? Based on this idea, we see the Gemara used the word, “yassaf” which connotes adding into the original of the same kind. The Maharal then answers that the Shabbos of Mara was added to the seven Noahide laws. Therefore the Shabbos of Mara was not a Jewish convental shabbos, just an additional law that was given to them as sons of Noah, not Jews. 

What is important about these three additional mitzvos that the Jews needed them specifically prior to Mount Sinai? Logic dictates that they must be a prerequisite to the receiving of the Torah. Be’er Mayyim Chayyim (Shemos 19:1) explains that the purest soul would be able to intuitively sense the commandments of the Torah, such as Abraham who kept the entire Torah. It is only the impurities of the soul that cloud this natural instinct and ability to perceive truth. While in Egypt, God gave the Jews a miraculous boost whereby they could temporarily achieve this level of intuitive understanding of the Torah. This is why we recite at the Seder, “Kadesh Urechatz - Santify and cleanse.” Usually the order is to cleanse prior to sanctification as a preparation. However, in the Exodus, the Jews were given this sanctification without preparation and without having earned it. This was a temporary state. This is why the verse (Shemos 15:22) states that the Jews “went for three days without water”, and the Rabbis allegorically interpret this as three days without Torah (water = Torah. Bava Kamma 82a.) 

What was the Torah that they were lacking? Be’er Mayyim Chayyim says they thirsted for this intuitive understanding of Torah which they achieved Pesach night (Kadesh, Urechatz) and now lost. At Mara, while the Jews could not fully restore this state, they were able to recover it vis a vis the mitzvos of Shabbos, honoring parents and the legal system. I will add, these mitzvos in particular represent intuitive commandments. Society requires hierarchy and authority, thus the legal system and honoring parents are essential ideas to internalize. And, for society to function well according to Torah thought, the members and especially its leaders, must hold themselves accountable to a higher moral authority, beyond petty human concerns. This is represented in the Shabbos, which honors and testifies that the World has a creator, who has expectations and standards. 

By following these prerequisite commandments, the Jews could attain a sanctification necessary to accept the full Torah later at Mount Sinai.