Day of Purification
We will examine Rashi's "lead word" - in Hebrew, "dibbur hamaschil." Each Rashi comment is introduced by a "lead word." Rashi's comment is based on it. These are printed in the Chumashim in bold letters. Rashi has his own style when it comes to "lead words." Understanding them saves us much time in trying to understand his commentary. Let us look at the first one in the Parshat Metzora.
"This shall be the law of the metzora on the day of his purification. He shall be brought to the priest."
In many printed Chumashim we find the following "lead word" in the first Rashi comment.
This will be the law of, etc. - Rashi: It teaches that he is not purified at night.
WHAT IS BOTHERING RASHI?
Rashi's comment seems clearly based on the words in the verse "on the day of his purification." The words "on the day" are unnecessary. The verse could have just written "in his purification." See verse 14:32 where this is what the Torah does say.
THE INCOMPLETE LEAD WORD
But what is strange is that the "lead word" does not contain the crucial words "on the day", upon which the interpretation is based.
UNDERSTANDING THE INCOMPLETE LEAD WORD
This can be explained by the word "etc." (in Hebrew "v'gomer"), which Rashi added at the end of the "lead word." This always means that the continuation of the verse, though not explicitly quoted by Rashi, is also important for his comment. So the "etc." here could refer to the words "on the day," which excludes night-time purification.
A CLOSER LOOK
But something else is strange about his "lead word" here, and by examining it we can learn something important to Rashi's Style with "lead words."
RASHI'S FIRST COMMENT ON EVERY PARSHA
As a rule, Rashi's first "lead word" in every parsha contains the words which are the name of the parsha. Check this out throughout the Torah. This rule holds true, with only one exception - see Parshat Kedoshim.
But our "lead word" does not contain the word metzora which is the name of the parsha. I noticed this recently. It looked strange, then I checked with a more precise Chumash and found that the full "lead words" said, "This shall be the law of the Metzora." So here we have the name of the parsha included in the "lead word."
Being aware of Rashi's custom of always beginning a parsha with a "lead word" that contains the name of the parsha explains some puzzling Rashi comments. See Parshat Beshallach in the book of Exodus and Parshat Vayelech in the Book of Deuteronomy. Here Rashi has only a "lead word" (which contains the name of the parsha) but no comment whatever. This has puzzled many commentators on Rashi. Some have come up with creative interpretations of why Rashi has no comment on those "lead words." But in light of what we said, there is no difficulty. Rashi wrote the "lead word" to mark off the beginning of a new parsha – even if he had no comment to offer on these words.
(By the way, this same custom holds for Rashi's comment on the Talmud. He always has a comment on the first words of each new chapter in the Talmud.)
Understanding Rashi's style is important for fully understanding his brilliant commentary.