After makkas bechoros, Hashem commanded Bnei Yisrael regarding their firstborn. "Sanctify for Me every firstborn of Bnei Yisrael, of man and animal, they are Mine" (Shemos 13:2). Rashi explains that the firstborn "belonged" to Hashem for He acquired them when he smote the Egyptian firstborn. What does the killing of the firstborn Egyptians have to do with the Jewish Nation?
Rav Wolbe (Shiurei Chumash, Shemos 13:2) explains that in truth it has everything to do with the Jews. The Novardakers would say that when one reads an obituary in the paper, he tends to think to himself that there is a segment of "people who die," but he himself is in no way connected to them. It is simply a quirk that they pass away and he himself is not destined for such a fate. It does not dawn upon him that indeed it has very much to do with him for he is surely destined to join that group sometime in the (hopefully distant) future.
The Baal Shem Tov would say that the world is like a mirror. Everything a person sees has something to do with him. If Heaven ordained that he perceive those things then they must in some way be connected to him. Like everything else, the smiting of the Egyptian firstborn was a lesson for all those who witnessed the phenomenon. Hashem was revealing to Bnei Yisrael that He acquired all firstborn and He specifically chose to kill the Egyptians and spare the Jewish firstborn. Therefore Bnei Yisrael were commanded to heed the lesson and be mikadesh the Jewish firstborn.
What is kedusha? Kedusha is that very same ability to take that which one perceives and make it pertinent to himself. Rashi on the pasuk, "For you are a holy people to Hashem" (Devarim 14:21), cites the Sifrei which explains the pasuk as a directive: "Make yourself holy with regard to those things that are permissible to you. If others prohibit something, you should not permit it in front of them." From the fact that the Sifrei defines such conduct as kedusha, it is clear that it is not merely an act of consideration for the feelings of others. Rather the Torah is instructing us to take heed of what you see around you. If you find yourself amongst people who are more meticulous in a specific area, you should apply that which you see to yourself. Try to emulate their deeds for at least as long as you find yourself in their company.
We might have graduated school, but we are always under Hashem's tutelage. He is constantly instructing us by way of the numerous occurrences that we witness throughout the day. Let us not fall asleep during His class. There is so much that we could learn and accomplish if we would apply that which we see to ourselves. If we witness someone's mistake we should realize that we are susceptible to such behavior and take the necessary precautions to prevent ourselves from wavering in that area. If we happen to hear about a person who is single who is looking for his bashert it might be a heavenly message that we have the ability to help them. An awareness of this concept allows one to look out a glass window and nevertheless see a reflection of himself.