For how long must a Jew keep Shabbat before he can be considered Shomer Shabbat?

Question

Certain Kashrut issues require (or may require according to some opinions) that a Shomer Shabbat Jew (not just any Jew) supervise cooking. For example, see here, and here.

How is the status of Shomer Shabbat formally defined? For example:

1) If Jew generally keeps Shabbat but slips up once in a while (maybe, once a month, or once every few months), is he still Shomer Shabbat or does any violation totally destroy his status?

2) If a non-Shomer Shabbat Jew suddenly decides to begin keeping Shabbat, does he become Shomer Shabbat immediately by the very decision itself (ipso facto) as long as his intent was genuine (e.g. he can immediately begin supervising kashrut and, if he dies, dies as a Shomer Shabbat Jew, even if he repents on Wednesday morning and dies before the arrival of the next Shabbat)? Does he only become Shomer Shabbat after keeping a full Shabbat? Does he have to observe a specific number of Shabbats? Two? five? seven? ten? An entire year? A hundred weeks?

As an analogy, the question could be considered similar to asking when a person who is in the process of quitting smoking officially becomes a non-smoker. For some insurance purposes, that has been defined as a year, but in many cases the social or medical definition may vary. Mark Twain infamously claimed that quitting smoking was so easy that he had done it a thousand times. Is Shomer Shabbat similar in that the exact determination of a person's status depends on social factors, or is there a sharp line in the sand? E.g. maybe Reuven has been faithfully keeping Shabbat for the past five years but is still not considered Shomer Shabbat by his synagogue and Rabbi because he had a forty year reputation as one of the most notorious, blatant, public, unrepentant, and generally in-your-face Shabbat violators in the Tri-State Area, even becoming world famous as the person who turned on and off the lights at the Saturday Morning Pork and Shellfish Cookout Competition and Idol-Worshiping Extravaganza every week for twenty years, and the Rabbi has ruled that he must complete ten whole years of observance to prove his repentance.

Answer 1

One can say that the question is how to know if someone did Teshuva.

The Gemara (Sanhedrin 25b) says

ואימתי חזרתן משישברו את פיספסיהן ויחזרו בהן חזרה גמורה דאפילו בחנם לא עבדי מלוה בריבית אחד המלוה ואחד הלוה ואימתי חזרתן משיקרעו את שטריהן ויחזרו בהן חזרה גמורה אפילו לנכרי לא מוזפי ומפריחי יונים אלו שממרין את היונים ולא יונים בלבד אמרו אלא אפילו בהמה חיה ועוף ואימתי חזרתן משישברו את פגמיהן ויחזרו בהן חזרה גמורה דאפי' במדבר נמי לא עבדי סוחרי שביעית אלו שנושאין ונותנין בפירות שביעית ואימתי חזרתן משתגיע שביעית אחרת ויבדלו וא"ר נחמיה לא חזרת דברים בלבד אמרו אלא חזרת ממון כיצד אומר אני פלוני בר פלוני כינסתי מאתים זוז בפירות שביעית והרי הן נתונין במתנה לעניים And when is their repentance accepted, so that they may resume being fit to bear witness? Once they break their pispasim and repent of them completely, abandoning this occupation entirely, where they do not do this even for nothing, i.e., they do not play even without betting. The baraita continues: The expression: One who lends with interest, is referring to both the lender and the borrower. Both are disqualified. And when is their repentance accepted? Once they tear their promissory notes and repent of them completely, abandoning this occupation entirely, where they do not lend with interest even to a gentile. The expression: And those who fly pigeons, is referring to those who induce the pigeons to behave in this manner, i.e., they train them. And the Sages did not mean to say that only those who fly pigeons are disqualified; rather, even those who do this with a domesticated animal, an undomesticated animal, or any type of bird are disqualified. And when is their repentance accepted? Once they break their fixtures [pigmeihen] upon which they stand the competing animals, and repent completely, abandoning this occupation entirely, where they do not do this even in the wilderness, where there is no one from whom to steal. The expression: Merchants who trade in the produce of the Sabbatical Year, is referring to those who do business with the produce of the Sabbatical Year. And when is their repentance accepted? Once another Sabbatical Year occurs and they refrain from selling its produce or from assuming ownership of such produce. The baraita continues: And Rabbi Neḥemya said: The Sages did not say that verbal repentance alone is sufficient for a merchant who traded in the produce of the Sabbatical Year to be reinstated as a valid witness; rather, returning the money is also necessary. How can one return the money he gained from selling produce of the Sabbatical Year? He says: I, so-and-so the son of so-and-so, gathered, i.e., profited, two hundred dinars from trading in the produce of the Sabbatical Year, and as I gained it improperly, this sum is hereby given as a gift to the poor.

Rashi says

דאפילו לנכרי - שישתכח שם ריבית מפיהם דתו ודאי לא הדרי לקלקולייהו: Even to a Non-Jew - That one should forget the concept of interest, so he won't come to sin.

And

לא חזרת דברים - לומר לא נוסיף עוד אלא חזרה הנכרת שיפזרו פירות שביעית שבגנותיהן לעניים:

Not verbal retraction - Not just saying that he won't stumble again, but a visible retraction, that he returns the (Shmittah) produce to the poor.

So it seems that one has to do a repentative action with a loss of money.

However, the Rama writes Choshen Mishpat 34:22 that

מומר שחזר בו וקבל עליו תשובה כשר מיד אע"פ שלא עשאה עדיין (מהרי"ק שורש פ"ה). An apostate who repents, we accept his repentance immediately even if he didn't do any actions yet.

And the Sema (34:44) says the reason:

Since they were surrounded by non-Jews (who have all the pleasures) and wants to separate himself from them, we don't act stringently with them and assume they fully repented.

However, this implies that a declaration of repentance only works when one is losing out. However, the Shach writes that we always accept the word of an apostate coming back right away.

The Piskei Teshuva says that he has to start repenting, and he should also do some self-mortification.

Answer 2

Lechorah I would answer your first question with the standard definition of a shomer shabbos, ie someone who is not mechalel shabbos befarhesiah, in open. That's the only way we know if he's a shomer shabbos. As far as I'm aware, there's no leeway given someone who "slips up". (Slipping up where a person is not aware its shabbos, or not aware that what he's doing is forbidden, assur, on shabbos is talked about and not considered chilul shabbos. It's a shogeg, mistake.) Slipping up as you are saying would be considered violating shabbos and if he does it in public, we dont consider him a shomer shabbos until he does complete teshuva and accepts completely to never do it again. (To be clear: Im saying in public, because in private we have no way of knowing what a person does, however, I'm not telling you you're keeping shabbos as long you cook your eggs undercover.) So, according to my own daas on this subject, not a psak, but anyone who ever "slips up" in public, even once in a lifetime, as long as he hasn't done teshuvah, is not trusted to be considered a shomer shabbos. A for what is considered teshuvah, see the other answer which quotes the gemara. The rambam quotes it as well. These are teshuvos for other public aveiros, forbidden activites. They aren't chiyuvei misah, and aren't considered an ois like shabbos is (a big issue), however I don't see why it's different by shabbos, unless someone can bring me a source or proof that it is, because teshuva works for shabbos and we don't see that it doesn't. However, I have not researched the issue and I stand to be corrected by anyone with a proof.