המשכיר בית לחברו--על השוכר להביא מזוזה ולקבוע אותה, אפילו היה נותן שכר על קביעתה: מפני שהמזוזה חובת הדר היא, ואינה חובת הבית. וכשהוא יוצא, לא ייטלנה בידו וייצא; ואם היה הבית לגוי, הרי זה נוטלה כשייצאThe fact that M'zuza is chovat haDar and not chovat haBayit explains why a renter and not the owner of a house has the responsibility to affix the m'zuza. If so, why is he not allowed to take the m'zuzot he purchased and affixed when he moves out? If it is chovat hadar his chiyuv ends once he leaves his residence so he should have no responsibility to keep the m'zuzot affixed.
In both this post and the previous one I seem to have entered the murkier waters of the Rambam. It is difficult to find the principle which would clarify such difficulties. I wonder, when b'nei yisrael received the Torah would the very way in which it was presented have made such anafim clear? It would seem that even though the fundamental principles would certainly have been clear to all of b'nei yisrael not every individual would have been able to discern how every anaf emerges (I mean immediately - of course this difficulty would cause them to pursue a dialogue with their Rav to clarify the issue)
Is this what is meant by na'aseh v'nishma? In other words all of b'nei yisrael possess the ikrei dat Moshe Rabeinu but not all of the anafim will be clear. It would seem that at least the generality of each mitzva would have clearly emerged from fundamentals for them (and it should for us). For example, m'zuza is a mazkir which is instrumental remembering and loving Hashem constantly and we need mazkirim rabim because we are prone to the cheit of viewing aretz as keri which we think we can lord over and mold to our own design, etc.