במדבר פרק ה

אברבנאל asks nine questions on פרק ה of ספר במדבר:

Within his answers to these questions, אברבנאל quotes a מדרש (beginning with "ובמדרש"):

The מדרש explains that those who are not permitted to enter the מחנות represent the three עברות for which בנ"י will be exiled from ארץ ישראל. The צרוע represents one who has committed the sin of עבודת כוכבים, the זב represents one who has committed the sin of גילוי עריות, and the טמא לנפש represents one who has committed the sin of שפיכות דמים. Since at this point, the nation is heading straight into the land, now is the time for them to purify the camps. What better what to do so than to purify it the way א"י is supposed to be purified? Since these three sins are the ones that will cause a member of the nation to be exiled from the land, these three types of people should also be exiled from the camps in the מדבר.

It is difficult to pinpoint exactly which question אברבנאל is addressing with this מדרש, but it seems like this explanation serves as one answer to his first question regarding why this law is placed here instead of in ספר ויקרא. Since this law is relevant to entrance into the א"י and the way in which the nation prepares for that event, the law is placed right before the nation is supposed to begin their journey into the land.