The Shema does instruct us to “love God with all your heart” and it would seem appropriate when this prayer references specifically one of the physical manifestations of our religion, “the fringes on the corners of the garments”, touching or even kissing that object.

But kissing as a demonstration of respect, as in kissing the ring of your Lord and Master, seems more historically appropriate. Particularly since the joys of face to face kissing (kissing for love) was not evident in the middle east or Europe until the 3rd century BC. (It is believed to have been brought back from the far East by Alexander the Greek. There are no references in Egyptian, Babylonian or Assyrian writings or art- almost nothing in Greek).

Formal references to the detailed rules about how to handle the tallit – including when to kiss the fringes and which hand to hold them in- seem to date from the 16th century CE, although they codify a practise that may have been around for a while.

Looked at from a historical vantage, another explanation for the attention paid to the fringes during this prayer (including gathering them in your hand while saying the Shema) makes sense to me. The prayer explicitly commands “you shall have the fringe so that when you LOOK upon it, you will remember to do all the commands of the Lord”. But it seems likely fringes were originally something that you wore at all times on your garment as a sign and a reminder -as today all Chasidic and most Orthodox Jews, do. If you wear fringes all the time, fringes become as routine or boring as socks.

Bringing the fringe up to your eyes – explicitly following the instruction to “LOOK” at them as special, seems a perfectly logical, even essential, corrolary to the prayer. And at that point, kissing the fringes as a sign of love, respect and recognition of their importance as a commandment and reminder seems almost inevitable. For an alternative, less appropriate way to demonstrate that you really are “looking”, see this classic Chevy Chase video clip: https://www.youtube.com/watch?v=AqNwo2NpmGY