6 He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it. He that eateth, eateth to the Lord, for he giveth God thanks; and he that eateth not, to the Lord he eateth not, and giveth God thanks.
7 For none of us liveth to himself, and no man dieth to himself.
8 For whether we live, we live unto the Lord; and whether we die, we die unto the Lord: whether we live therefore, or die, we are the Lord's.
9 For to this end Christ both died, and rose, and revived, that he might be Lord both of the dead and living.
10 But why dost thou judge thy brother? or why dost thou set at nought thy brother? for we shall all stand before the judgment seat of Christ.
11 For it is written, As I live, saith the Lord, every knee shall bow to me, and every tongue shall confess to God.
12 So then every one of us shall give account of himself to God.
Jews did not celebrate birthdays. Pagans did. On only 2 (maybe 3) birthdays in Bible, someone died. Pharoah’s, Herod’s, and perhaps Job’s first children.
Early Christians did not celebrate Jesus birth for first one or two hundred years, and even condemned the practice when pagans wanted to introduce it.
We are specifically instructed, on the other hand, to celebrate not His birth - but His death - often. The dates of His birth or death are not important. What occured in his death is all-important. Our salvation. Proven by His resurrection.