Religion shapes daily rhythm far more in some countries than others, and gauging that early helps you avoid missteps. In much of the Middle East, South Asia, Southeast Asia, and Africa, faith is woven into schedules, food, dress, and law: prayer times structure the day in Muslim countries, with Friday as the holy day and weekends often falling Friday-Saturday; fasting during Ramadan changes business hours and makes daytime public eating a sensitivity; and alcohol may be restricted or absent. Buddhist and Hindu societies fold temple life, festivals, and food customs like widespread vegetarianism into the everyday. Elsewhere, particularly much of Europe and East Asia, religion is more private and its main public traces are holidays and architecture.
What travellers should know regardless of destination: the major holidays and any fasting periods, since these move dates on lunar calendars and affect opening hours, transport, and mood; dress and behaviour rules at religious sites, typically covered shoulders and knees, shoes off in many traditions, and quiet respect; and food rules, including halal, kosher, vegetarian norms, and beef or pork sensitivities, which matter when hosting or giving gifts.
Check a reliable guide for your specific country's religious calendar and etiquette, and when invited to any observance, attend respectfully, follow your host's lead, and treat it as the privilege it is.