The Damasek Eliezer of Vizhnitz, zt”l, was very particular that the bochurim in his yeshiva should always kiss the mezuzah as they entered and exited a room. When asked why, he explained: “It is well known that when a lower ranking soldier encounters an officer he must salute him to show that he is under his authority. If a soldier refuses to do so for any reason he is in danger of being severely punished since he refused to recognize the officer’s rank. “The rule is that the supernal kingdom is patterned after earthly kingship. Since the mezuzah declares Hashem’s unity and Hashem sits outside and guards us through the mezuzah, we must be fastidious to kiss it when we enter or leave a room. In this manner we show that we accept Hashem’s kingship on ourselves.” Interestingly, the Maharil Diskin, zt”l, appointed messengers to go from door to door and check each house’s mezuzos to ensure they were really kosher. Since he used money slated for the orphans under his care for this as well, many people wondered how this was permitted. After all, the halachah is that money slated for orphans should not be used for other purposes. When Rav Bentzion Yadler, zt”l, asked the Maharil Diskin about this, he explained, “The verse states that we should put mezuzos on our doors 'למען ירבו ימיכם'. So if I ensure that people’s mezuzos are kosher, the parents will live longer and there will be fewer orphans. Obviously, this is permitted from the money slated for orphans since the less orphans there the more money there is for each one’s use!”