In I Corinthians 10:19-21, the apostle Paul compares mixing paganism with Christianity—syncretism—to worshipping demons. This principle includes giving one's time or interest to things of pagan origin.
As an example, the Bible neither mentions nor espouses Valentine's Day or its practices. However, God informs ancient Israel in Deuteronomy 12:29-31 that He had chosen them to represent true religion, and He warns them not to mix pagan customs with worshipping Him as the one true God:
When the LORD your God cuts off from before you the nations which you go to dispossess, and you displace them and dwell in their land, take heed to yourself that you are not ensnared to follow them, after they are destroyed from before you, and that you do not inquire after their gods, saying, “How did these nations serve their gods? I also will do likewise.” You shall not worship the LORD your God in that way; for every abomination to the LORD which He hates they have done to their gods.
Beyond their obvious heathen origins, holidays like Saint Valentine's Day continually secularize, transforming into reflections of the world's present culture and falsifying the religions from which they sprang. Most people in this world, becoming increasingly materialistic, could not care less if Valentine's Day originated in the Roman Lupercalia or early Roman church doctrines. Religion—true, syncretized, or pagan—has little influence on them. All they care about is whether they enjoy the celebration. This apathy about how to worship the true God and its corresponding moral decay is the result of watering down truth, minimizing its authority, and appealing to people's base desires, that is, their human nature (Romans 8:7; I John 2:16).
Even some Christians who reject religious holidays with roots in paganism, like Christmas and Easter, see nothing wrong with holidays like New Year's Day, Valentine's Day, and Halloween despite their pagan origins . Their faulty human reasoning—their rationalization or justification for it—goes like this:
Christmas and Easter must be rejected because they attempt to worship God with pagan customs. The other holidays, though, while people may have once used them to worship God, are now deemed entirely secular. And since God actually forbids using pagan customs to worship Him, we are free to practice pagan worship customs if we are not now using them for worship purposes.
Yet, this bit of twisted logic ignores the fact that God tells the Israelites to eradicate all vestiges of pagan worship from their presence (Deuteronomy 12:2-4), not merely from their worship of Him. Moreover, the New Testament teaches that a Christian's life is to be one of worshipping and honoring God in all we do (I Peter 4:11).
We should see the things in which we participate in the context of bringing glory to Him. This does not mean we cannot have fun; God wants us to enjoy life. But our fun should not be independent of Him (see the principle in Ecclesiastes 11:9). All that we think, say, and do should be to the glory of God (I Corinthians 10:31)!
No true Christian in good conscience would want to be someone's Valentine, and he certainly would not wish someone a “Happy Valentine's Day!” We must speak the truth in godly love (Ephesians 4:15), not carnal lust. In its fleshly and sensual practices, Valentine's Day falls far short of “worship[ping] the Father in spirit and truth” (John 4:23).
