why do we celebrate birthday ? what is the function of its.?

hello dear my steemit friends, today i was reading one book, in which i have read that we should not celebrate happybirth day becasue if we think that one year has been cut off from our life, but with example the writer briefly explain how our life is going to end,, and we celebrate that one year from our life gone, and we got pleasure on this .

writer mentioned that one baby born then get young age, adult then old,, its mean he is growing but after growing again go to age of child.

writer gave many beautiful example in this regards. for example , when any old person ,age of 80, he/she has no ability to move freely, he/she can not see well, also not hear. can not understand thinks, can not read, write,, this ratio is 99%, yeah it is also correct, my grandmother was 80 years, but could not do, move,, so our all family treated her with like small new born baby,,

"The idea of celebrating the date of your birth is a pagan tradition. In fact, many Christians didn't celebrate birthdays historically, because of that link to paganism. Pagans thought that evil spirits lurked on days of major changes, like the day you turn a year older"
do you all agree with me,, or not please tell me writer is true or not,, need your help in comments,

thanks reading me dear all.