Instead of cowering behind a fear of being corrupted by paganism and risking incurring God’s wrath, it’s important to see this issue in the light of the New Covenant given to us through Jesus’ sacrificial death on the cross.
Jesus said, "If you are kind only to your friends, how are you different from anyone else? Even pagans do that." (Matthew 5:27 NIV) Should we then not show kindness at all, because we don't want to be associated with paganism?
Reread the passage -- Jesus isn't telling us not to do what the pagans do, but to live our lives in such a way that brings honor to Him, that if people found out we were Christians, they wouldn't be surprised at all. No, we are not to call ourselves Christians, yet continue to live sinful, worldly lives. Instead, we are to “Live such good lives among the pagans that, though they accuse you of doing wrong, they may see your good deeds and glorify God on the day he visits us.” (1 Peter 2:12)
Don't just be kind only to your friends, but be kind also to strangers, even to your enemies. Live your life with a heart of love, not love merely reserved for those who love us, but for all, unconditionally and radically.
Likewise, don't not celebrate Christmas because it's "pagan." Don't only celebrate it on December 25th. Celebrate it every day in the way you act, talk, live!
“In the same way, some think one day is more holy than another day, while others think every day is alike. You should each be fully convinced that whichever day you choose is acceptable. Those who worship the Lord on a special day do it to honor him. Those who eat any kind of food do so to honor the Lord, since they give thanks to God before eating. And those who refuse to eat certain foods also want to please the Lord and give thanks to God. For we don’t live for ourselves or die for ourselves. If we live, it’s to honor the Lord. And if we die, it’s to honor the Lord. So whether we live or die, we belong to the Lord. Christ died and rose again for this very purpose—to be Lord both of the living and of the dead.” - Romans 14:5-9
“For why should my freedom be limited by what someone else thinks? If I can thank God for the food and enjoy it, why should I be condemned for eating it? So whether you eat or drink, or whatever you do, do it all for the glory of God.” - 1 Corinthians 10:29b-31
What “pagan” customs should we stay away from?
“For you have spent enough time in the past doing what pagans choose to do—living in debauchery, lust, drunkenness, orgies, carousing and detestable idolatry. They are surprised that you do not join them in their reckless, wild living, and they heap abuse on you. But they will have to give account to him who is ready to judge the living and the dead.” - 1 Peter 4:3-6 NIV
“Israel failed to destroy the nations in the land, as the Lord had commanded them. Instead, they mingled among the pagans and adopted their evil customs. They worshiped their idols, which led to their downfall. They even sacrificed their sons and their daughters to the demons. They shed innocent blood, the blood of their sons and daughters. By sacrificing them to the idols of Canaan, they polluted the land with murder. They defiled themselves by their evil deeds, and their love of idols was adultery in the Lord’s sight.” - Psalm 106:34-39
Jesus said, “It’s not what goes into your mouth that defiles you; you are defiled by the words that come out of your mouth… the words you speak come from the heart—that’s what defiles you. For from the heart come evil thoughts, murder, adultery, all sexual immorality, theft, lying, and slander.” (Matthew 15:11,18-19)
Whether you eat or drink, or whatever you do, do it all for the glory of God!