
What are holy days?
Here's the answer:

Holy days are days set apart to focus on the Lord.
The holy days of the Bible include Passover, Unleavened Bread, Firstfruits, Pentecost/Weeks, Trumpets, Tabernacles/Booths, Purim, and the Day of Atonement. These holy days are also known as festivals or feast days. They were required in the Old Testament under the Jewish Law, but as believers, we are not under this mandate anymore. This means we don't have to celebrate holy days.
If a person wants to celebrate holy days, then that is completely okay. Paul tells us, “One person considers one day to be more holy than another. Another person thinks all days are the same. Each of them should be absolutely sure in their own mind” (Romans 14:5). Therefore, if someone wants to celebrate a holy day, that is fine, and if they don't, then that is fine, too.
What ultimately matters is that we live each day as a holy day. When we wake up in the morning, we should try to live for Jesus and bring glory to His Name. This is radically different from just calling a day a holy day. Practicing living holy days will change our lives and help us to follow Jesus faithfully.

Bible Truth
"The Lord said to Moses, 'Speak to the Israelites. Tell them, "Here are my appointed feast days. They are the appointed feast days of the Lord. Tell the people that they must come together for these sacred assemblies"'" (Leviticus 23:1–2).
"So eat and drink and do everything else for the glory of God" (1 Corinthians 10:31).