“Love the Lord with all your heart, and with all your soul,
and with all your MIND”--Matt 22:37
Question: Why do Catholics celebrate Christmas on Dec. 25? "The Bible does not give the exact date of Jesus’ birth. Furthermore, it indicates that Jesus was born, not in the cold, rainy month of December or January but in a warmer season"--as argued by the Jehovah's Witnesses (JWs).
Short answer: it is indeed an arbitrary (although rooted in tradition) date chosen by the Catholic Church to celebrate our Savior's birth, as the exact day of Jesus' birth is unknown.
I would just like provide a cautionary statement: while it is our baptismal duty to share our faith--indeed, our faith is NOT private and we ought to invite others into the fullness of the Truth--JWs are not allowed to read any materials we Catholics might offer to them. Thus, it is really a one-sided dialogue that often occurs, with the JWs offering their arguments against Catholicism, but being unable to engage us in hearing our apologia. In addition, JWs are very adept at proclaiming their false doctrines. Many a person has succumbed to their astute missionary/biblical expertise and can be left with questions that are seemingly answered only by JW doctrine.)
Now, back to the discussion at hand!

Thus, the Church does not proclaim that Jesus was actually born on Dec. 25. Only that we celebrate it on this day. It's a celebration of the Incarnation, not a memorial of a specific day.
It is also true, as the JWs contend, that Dec. 25 was a pagan holiday, to celebrate the winter solstice. It is because this pagan origin that JWs do not celebrate Christmas (not to mention JWs do not believe Jesus is God, and thus reject the doctrine of the Incarnation.)
However, while the origins of the date of Christmas may have begun on a pagan holiday, Christianity reformed this pagan date date and made it holy! Indeed, this is a similar paradigm to the Incarnation. 2000 years ago Christ entered this pagan world and reformed and sanctified it by His Presence!
"Early Christian worship often used the customs and symbols associated with the paganism around it. One instance: The fish was a symbol of fertility in the ancient world and of eroticism in particular for the Romans. This pagan symbol became one of the most important symbols of the Church, the Greek word for "fish," ichthus, becoming a condensed confession of the faith....
Here was an opportunity for the Church to confront paganism, and so it aimed at one of the biggest and most important cults in Rome. The day chosen was December 25, when everyone celebrated the pagan feast of the dies natalis Solis Invicti, "the birthday of the Unconquerable Sun."
December 25 arrives around the time of the winter solstice, when the days get shorter and the sun seems to be "dying." After the winter solstice, the sun appears to regain its strength, is "born again" as it were, as the days become longer. Consequently, December 25 was the "birthday" of the Persian sun-god known as Mithras, originally one of the lesser demigods of the Zoroastrian religion. Mithras had become the principal Persian deity by 400 B.C. and his cult quickly overran Asia Minor. According to Plutarch, it was introduced into the West around 68 B.C., and became quite popular among the Roman legions." source
(Disclaimer: please note my comments on JW doctrine ought to be taken with the same grain of salt as if you heard JW claiming "This is what Catholics believe." I have a very limited understanding of JW doctrine...BUT! I also don't think I'm wrong in what I've been saying so far about JWs.
