Brother,
That verse is speaking of food and men who limit what they can eat on certain days. Here is short study on it and a link to a much longer study not written by myself.
"Romans 14:5-6
5 One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind.
6 He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it. He that eateth, eateth to the Lord, for he giveth God thanks; and he that eateth not, to the Lord he eateth not, and giveth God thanks.
Some people try to use these verses to say that since Paul said, both the man who esteemeth one day above another and the man who esteemeth every day alike, to say that what days we keep have no more significance except to those who believe it remains.
But when we look at these verses in context we see that Paul is speaking of only two things: 1. Weaker and stronger brethren 2. What foods are clean and how they are made clean.
It is in the light of the surrounding verses that we see what Paul is speaking of in verses 5-6. He is speaking not of the Sabbath day, or of Christians being able to keep any pagan holiday or custom they wish to, but of people who are weak in the faith and decide in their hearts that the Lord does not want them to eat certain things on certain days. There are many studies on these two verses that can be found online that show that what Paul was speaking of here was not the Sabbath day or being allowed to keep Pagan customs, but instead of those who chose to limit what they could eat on certain days.
While I do not agree with this Church's(Seventh Day Adventists) views on the translation of the Greek word used for unclean in romans 14
2839. Koinos
Translated as Unclean but could also mean: common, defiled, unclean, unholy.
I do agree with most of what they have to say about Romans 14:5-6 and they provide an excellent commentary/Exegesis on it here:
https://adventistbiblicalresearch.org/sites/default/files/pdf/Onedaybetter.pdf"
We are to judge all things by the spirit(Matt 7:1-3) Because all will be Judged by the word of God in the Last day. So also are Christ followers to judge all things by the word of God and by the same word will they be judged(1 Cor 2:15, 6:2-5).
A man who chooses to adopt a Pagan Holiday/Custom as the Lord's has everything to do with his fellow brethren, since we are to correct those who fall away from God's teachings and remove ourselves from them if they do not listen(2 Thess 3:4-6; Galatians 6:1-2; 1 Timothy 5:20-22; Romans 16:17-18). By choosing to keep ungodly traditions they break the commandment instituted by God(2 Cor 6:14-17, Eph 5:11-12) that we are to be separate from the world and it's customs/traditions(1 John 2:15-17,3:1,4:4-8,16, John 17:1-26[Especially 12-19], 15:16-27) keeping only the things of the Spirit.
I speak only to correct wrong as we are commanded to do. If a person adopts ungodly practices we are to tell that person how and why they are wrong so that they may turn from their evil ways and back to righteousness.