In the Bible the kiss is more than a simple greeting.  It is an expression of affection, devotion, and reverence. There are many examples: Esau and Jacob kiss after not seeing each other for a long time; Aaron kisses his brother, Moses; Samuel, kisses King Saul; Orpah kisses Naomi, her mother-in-law.

Since Bible days, holy objects have been saluted with a kiss to indicate affection and loyalty to God.  The Torah is kissed by the worshippers when it is carried by in a synagogue procession or by an individual when he recites the blessing over it.

Sephardic Jews, wave their hands towards the Torah, when they are not close enough to kiss it.  The Mezuzah is touched and kissed by one entering or leaving a house.  The fringes of the Talit are kissed whenever a person dons one.  When a holy book is dropped, it is kissed after it has been picked up from the ground.

Today, local customs vary.  Perhaps among the more interesting customs is that followed by Russian Jews, who use the index finger to kiss the Mezusah and the little finger to kiss the Torah scroll.