Thou shalt not do so unto the LORD thy God
Thou shalt not do SO - meaning "in that manner". What manner? Enquiring after the pagan religious customs, as to how they worshipped their demon gods.
Thou shalt not do so UNTO THE LORD - you shall NOT take pagan religious customs and ADAPT THEM TO THE WORSHIP OF THE TRUE GOD. It is EXPRESSLY FORBIDDEN.
Repurposing pagan holy days, and ceremonies, to the worship of God, is SIN.
What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it.
God has ordained the worship He wants us to give Him. It is in the Bible. We are not allowed to "add" or "take away" from the worship He has ordained. If you think you can take pagan religious practices and offer them to God, if you think He accepts such vain will-worship, YOU ARE MISTAKEN. It is ABOMINABLE to God. He literally HATES it.
"Oh, but God hears all my prayers, even though I'm steeped in pagan traditions!"
2 Thessalonians 2:11-12 KJV (11) And for this cause God shall send them strong delusion, that they should believe a lie: (12) That they all might be damned who believed not the truth, but had pleasure in unrighteousness.
God will make sure you believe lies and are damned, if you reject the truth of His Word.