Did you have a choice of cash or stock?
What did the company tell you about tax consequences?
In the case of other life insurance companies that demutualized and issued shares to policyholders, the shares issued were NOT taxed as income on distribution. However I am not sure of the "basis" the shares were given, or the tax consequences on sale of the shares.
In any event consider yourself lucky. You're getting essentially "free money" you never would have seen if it had not demutualized, nearly all of which was contributed by generations of policyholders who are long deceased. If you won the lottery -- and in a sense you did -- it would be taxable.