Re: "...Yacov: << I just don't understand why people celebrate things of pagan origin..."
Many brilliant books have been written dealing with this exact question, from the perspective of the modern sciences of psychology and psychiatry.
It seems that there are many "themes" dwelling deep within the most hidden recesses of humankind's collective subconcious minds.
These psychological "themes" have long been repressed by the demands made on us by modern lifestyles, yet the same basic "animalian" type of thoughts/impulses remain within all of us.
Most of them are made manifest and reoccur in the various mythologies and cosmological explanations of nations and peoples worldwide.
It is generally accepted today by scientists who study behavior that these "universal" subconcious links to our primordial history, always repressed, are "triggered" by various cultural stimuli, at which time they overpower our reasoning and cause us to revert back to our primordial memories.