Churches are seen as a safe haven and seldom a place of danger, so how can they be guarded, especially if they are known to always have their doors open?
Many are on edge across the world following the attack in Normandy, France, where an 86-year-old priest was killed by "Soldiers of ISIS," who forced the man to kneel before slashing his throat.
Inside America’s most renowned church, St. Patrick's Cathedral in New York City, security was tightened, as anti-terror police were seen in and around the structure that already has a bag check upon entering.
Security expert Nick Casale told Inside Edition: "We are not going to make the houses of worship impregnable because that takes away the concept of why you go to a house of worship. We are not going to give in to these savage terrorists."
Casale advises churchgoers to "remain vigilant" and be "suspicious of things that are out of the ordinary."
Many worshippers inside the famous Fifth Avenue cathedral were horrified to hear the news of the latest attack in France.
One visitor to St. Patrick's Tuesday told Inside Edition: "We are horrified by the idea that anybody is killed anywhere, but in a church, a sanctuary?"