The one who observes the day, observes it in honour of the Lord. The one who eats, eats in honour of the Lord, since he gives thanks to God, while the one who abstains, abstains in honour of the Lord and gives thanks to God.
Romans 14:6 ESV
In this passage, the apostle Paul is writing about those who are strong and weak in faith. This manifested itself in a couple of ways- to do with “holy days” and vegetarianism. These were different to how we understand them today, so contextualisation is required.
For Jewish believers, they had a rich tradition of holy days and festivals to remind themselves of God’s goodness to them throughout their history. To continue observing them is in honour of the Lord. But there’s no requirement even for a Jewish believer to observe Jewish feast days any more than Gentiles have to.
Note that when Paul writes about holy days, he’s not on about Christmas and Easter, which Roman Catholics would invent many years later to syncretise pagan festivals to make their faith more attractive. Of course, there’s nothing wrong with celebrating Jesus’ birth, death and resurrection. We just need to make sure that we celebrate thankfully and to honour the Lord.
The other issue is vegetarianism. In Paul’s day, Gentile converts from paganism wanted to avoid food sacrificed to idols. It’s like a Muslim background believer avoiding halal food by being vegetarian. So it’s not like people today who are vegetarian because they think the world will end if we keep eating meat!
“Lord, we thank You that there’s room for weak and strong in Your kingdom. Thank You that there’s freedom to observe days or not; to be vegetarian or not. Please help us to respect one another and to honour and be thankful to You. In Jesus’ name, amen”