Though the question is not without answers, one is still left wondering why Tzelophad’s daughters had to mention that their father died for his sin (27:3). As Ramban puts it, it would have been more fitting to simply say that he died without having male offspring. This would seem to be enough information to set up the problem that they were presenting in front of Moshe.
Besides the dishonor to their father created just by mentioning his sin, their utterance began a historical search to determine what that sin was. The most famous conjectures are that which Rashi cites from the Gemara (Shabbat 96-7): That it was either gathering wood on Shabbat or going along with the adventurers that wanted to conquer the Land of Israel right after the sin of the spies and God’s subsequent postponement of the conquest. While we are not told what the significance of either of those sins might be, Rashi makes the point that neither was a sin that led others astray. According to this, Moshe would have already known that their father had sinned. The daughters simply wanted to put it in the best light and distinguish it from more grievous sins that may have impinged on their claim.
While the above approach is plausible, many commentators have considered it removed from the simple meaning. Starting with R. Yehudah HaLevi, these commentators have understood the mention of their father’s sin to be a more general expression that could have been said about almost anyone. Indeed this comes in the context of Moshe being punished for his sin not too much earlier in the narrative. This approach seems to be especially popular among some of the modern commentators who expand upon it (R. Hirsch, Reggio, Shadal).
Accordingly, the Talmud (Shabbat 55b) states that all but four people died as a result of sin. That is to say that even though death is decreed for all men, everyone except for these four men would have died regardless of that decree. That being the case, the daughters of Tzelophad were not giving Moshe much new information. Nevertheless, since it was at least theoretically possible that Tzelophad had joined the tiny club of those that died without sin, it would be pertinent. Hence these women wanted to come clean. They didn’t want to pretend that their father was perfect. And by doing so they were granting the legitimacy of Moshe’s investigation into his life. In other words, they were saying that while he was not one of the tremendous sinners of the day, he was not without reproach – or as they said it, “he died for his sin.” This was an acknowledgement of the possibility that his actions would have a negative impact on their case. Not because he was a terrible man, but simply because he was a sinner – like everybody else.
This notion that we are all sinners may sound quite Christian. While the example of the Talmud’s four who did not sin may well show a theoretical difference between Christianity and Judaism, it cannot be said to be highly significant on a practical level. (Kohelet 7:20 implies as much.) The real difference is to what extent we find this state of common sin acceptable. In Judaism, since sin is not a foregone conclusion, we hold ourselves fully accountable for it. Likewise do we hold others accountable – if not to us, then certainly to God. And so the daughters of Tzelophad put this out about their father – and about everyone else.
Though there is an obvious danger of being overly zealous about the sins of others, a world that accepts sin as the natural state of things is a world that cannot truly improve. And that is why Judaism makes the point that we must constantly strive to remove it from ourselves and from others. By relating to the sin of their father as if it were an anomaly when it really wasn’t, these great women may have been making this very point. If so, it may well be especially to this that God tells Moshe (27:7), “The daughters of Tzeleophad speak truly.” Very truly indeed!