Psalms 51:5
Psalms 51:55Surely I was brought forth in iniquity; I was sinful when my mother conceived me.
JWs cite as background for Origen's argument that birthdays are inherently sinful — Origen read the verse as meaning conception itself is stained, so only sinners rejoice over their own birth. The Watchtower's Reasoning From the Scriptures preserves Origen's logic at second hand when explaining why birthdays are "not to be celebrated by Jehovah's Witnesses."
The verse describes the human condition under sin from conception — every Christian tradition agrees on this much. But Origen's leap from "sinful from conception" to "celebrating one's birth is sinful" is not an inference the verse can carry. Babies are born under Adam's curse, but they are still made in God's image, still "fearfully and wonderfully made" (), and still occasions for joy. prophesies that many will rejoice at John the Baptist's birth, and and curse the day of one's birth precisely because cursing it is a way of cursing one's whole existence — which presupposes the day was normally blessed. Origen himself was posthumously declared heretical for unrelated views, and Gregory of Nazianzus delivered birthday panegyrics; the church catholic never adopted the conception-to-birthday inference Watchtower teaching now requires.