While there is technically no obligation to tie tzitzis if one does not wear a 4-cornered garment, it is well-known that Jews have always made it a point to create that obligation by obtaining and wearing a ‘talis katan’ throughout the day. We wish to be surrounded on all four sides by that great constant reminder of the 613 mitzvos, as the Torah states in Bamidbar Chapter 15. In fact, this idea is symbolized by the 5 knots (the 5 chumashim) on each of the 4 corners (the 4 directions of the world.) In fact, the Mishnah Berura compares this to the common practice people have of tying strings around their finger to remind themselves of certain things! The Shulchan Aruch writes that it is even meritorious to wear the talis katan over the outer garments! (Ed: I have seen some people do that.) At the very least, we must wear tzitzis during tefila, which is why we all wear a ‘talis gadol’ at that time. The Mishnah Berura wrote bemoaning the fact that some people in his day would leave their davening talis at home when they traveled.
The Shulchan Aruch completes the entire section on the halachos of tzitzis (simanim 8-24!) with several minhagim involving our tzitzis during the recitation of Krias Shema:
1) Holding the four tzitziyos close to the heart during the entire Krias Shema. This practice is alluded to in the words: ‘v’hayu had’varim ha-eileh… al levavecha’ (…”let these words… be upon your heart”), because, as stated, the tzitzis remind us of the words of Torah. The Ariza”l instructed us to hold the tzitzis in the left hand; then, when reaching the third paragraph, to take them also in the right hand, and hold them out so that we may look at them. We should continue to hold them until we reach the word ‘la’ad’ (forever) in the bracha following the Shema, whereupon we kiss them and let them go from our grasp.
2) Looking at the tzitzis when making the bracha right before donning the talis.
3) Looking at the tzitzis when saying the words ‘ur’isem oso’ (you shall see it), then placing them upon the eyes and kissing them.
4) Kissing them also whenever we say the word tzitzis or Emes. Kissing a mitzvah object expresses our love for mitzvos!
When one looks at the front two tzitzis before him, he sees ten knots, which symbolize the Ten Sefiros (emanations) which are all interconnected, and sixteen strings. Together this adds up to the number twenty-six, which is the numerical equivalent of the four-letter ineffable Name of Hashem.
Finally, great is the punishment for one who does not wear tzitzis when he is obligated. Even greater is the reward for one who does wear them: he merits to see the Shechinah (Divine Presence)!