Theme comes with 2 different types of Lightbox options. Lightbox is used to display full size images in a popup. This is used for the gallery posts of the website. Option for the lightbox can be found at WP Dashboard => Native Church => Theme Options => Lightbox Options

Among these 2 options, Magnific Popup is the new script which is better in terms of responsiveness. On the other side PrettyPhoto is an older option but comes with some additional custom settings like different theme styles, background opacity etc.