Benzyl alcohol, although a primary alcohol, reacts very rapidly in the presence of hcl forming benzyl chloride. why is this?

Benzyl alcohol, although a primary alcohol, reacts very rapidly in the presence of HCl forming benzyl chloride. 

Because the positive charge is delocalized around the benzene ring. A free H⁺ ion attacks the lone electron pair on the OH⁻ and forms H₂O, which is a good leaving group. This is the reason why the reaction is fast.