According to the Mishna (see above, daf 68), one is liable to bring a sin-offering for each individual prohibited labor that he performs on Shabbat.
The Gemara asks:
From where do we derive the division of labors? What is the source of the halakha that if one performs numerous prohibited labors on Shabbat in the course of one lapse of awareness, each prohibited labor is considered a separate offense with regard to punishment?
Shmuel said that the verse says: “And you shall observe the Shabbat, for it is holy to you; he who desecrates it shall surely die [mot yumat]” (Shmot 31:14). We learn from the double language, mot yumat, that the Torah amplified multiple deaths for a single desecration.
According to this reading, although several violations were committed in the course of a single lapse of awareness, each is considered a separate offense with regard to punishment.
This source is deemed problematic by the Gemara since that verse was written with regard to intentional transgression; the Gemara is seeking a source for multiple sacrifices brought for unwitting transgression.
The Gemara explains the method from which it was derived:
If it does not refer to the matter of intentional transgression, as the verse does not teach a halakha applicable to intentional acts, as it was already written: “Six days you shall perform work, and on the seventh day it shall be holy to you, a Shabbat of rest to God; all who desecrate it shall die” (Shmot 35:2), refer it to the matter of unwitting transgression.
This form of reasoning – “if it does not refer to X refer it to the matter of Y” is one of the thirty-two hermeneutic principles of Rabbi Eliezer, son of Rabbi Yosei. According to most commentaries, the conclusions drawn from them are as authoritative as they would be if they were explicitly written in the Torah. This principle is based on the superfluity of verses in the context in which they are written. At the same time, the verse is never applied to matters totally unrelated to the meaning of the verse.
Thus, the verse teaches that that which was written with regard to the death penalty for desecration of Shabbat in general applies to all halakhot of Shabbat, including cases of unwitting transgression..