These days were given by the Lord and designed to be a prophetic calendar for his kids. They are not Jewish holidays. However, it turns out that by and large the Jewish people are the only ones keeping them. "Speak to the Israelites and say to them: ‘ These are MY appointed festivals , the appointed festivals of the Lord, which you are to proclaim as sacred assemblies." The apostle Paul said to the Gentiles "you received God’s Spirit when he adopted you as his own children."