Santa Claus involves a fictitious man who lives at the North Pole, having elves as helpers, and reindeer that fly. In this sense Santa Claus is an unrighteous fable rooted in dishonesty.
The notion of Santa Claus is problematic. One would be hardpressed to envision Santa Claus without reindeer, elves, and Santa delivering gifts. But reindeer, elves, and Santa delivering gifts involve dishonesty and pretense. These pretenses facilitate commercialization and removal of the focus from Jesus and God as the giver of gifts to children. It would be best for children to be told from the start who gave the gifts and that they are given in remembrance of the gift God gave and the wise men and shepherds gave and similar activities rooted in truth.
The major problem with the Santa Claus presentation is that in far too many cases children up to a certain age are led to believe Santa is real. Thus, the bad moral of dishonesty is practiced between parent and child, etc.
The little leaven leavens the whole lump principle speaks to this dishonesty.
Leaven is any ingredient that is undesirable for all situations/activities or at a particular time or for a particular purpose. Thus, God told the Jews to prepare unleavened bread (bread without using yeast) during the Passover. At other times and for other purposes it was holy to prepare leavened bread.
Here God uses leaven to symbolize that which is sinful, impure, undesirable.
Paul mentions this principle in 1 Cor 5:6-8 in speaking about the sin of a man having his father’s wife. Here Paul tells them to purge the congregation of that leaven (sin) even to the point of expelling (ex-communicating) the man if he refuses to repent.
Santa Claus to include honoring the original Saint Nicholas is not essential to the Christmas celebration. It is more of a distraction from focusing on Jesus as being the reason for the season and God as the bearer of the celebrated birth.
Santa Claus as practiced is a leaven of dishonesty. Santa Claus as practiced should be removed from the Christmas celebration. Christians should not pretend that Santa Claus is real.
Christians can easily avoid pretending Santa Claus is real in places like the home and church. They can teach there children about the true Christian purpose of Christmas and the unrealness of Santa Claus. Parents can tell children Santa Claus is made up by men for entertainment purposes. Santa Claus is not mentioned in the scripture by name but such entertainment is allowed by scripture providing it is made clear it is pretense and provided no immoral things are said or done.
Children will most likely encounter Santa Claus in schools, shopping centers and similar places during the Christmas season. In this case, parents can tell their children to think of Santa Claus as entertainment like a video game always keeping in mind he is just a man pretending to be from the North Pole, etc. Children may participate in the entertainment knowing Santa Claus and his elves and flying reindeer and related imaginary things are only for entertainment purposes. Parents should consider ensuring the school makes provisions for their children not be required to participate in activities that require them to acknowledge any realness of Santa Claus. They may participate if there is understanding between teacher and student that the student is only pretending for entertainment purposes. This approach is consistent with that which speaks about thinking on those thing that are true. It is consistent in that pretending something to be true for entertainment purposes that is known to be untrue is truth. Otherwise, reading a fiction book or playing most video games or watching most TV shows would be unholy. The way the parents handle this will differ at various ages of their children.
This does not mean it is unholy to give/exchange gifts as part of the Christmas celebration. It does mean for the Christian the teaching/representation of gifts should be that these gifts are given in the spirit of God giving Christ and Christ giving his life, all for the believer’s salvation. The gifts are to be an expression of God’s love and our love. The cost of the gift should not be important less the celebration be commercialized. Indeed, a visit as the shepherds did (Luke 2:15-17), phone call, or card or any number of things the person associates with Christmas qualifies as a gift.