This is actually the last issue of Detective in the Silver Age, dated December 1970. For those who weren't around then, this was the heyday of the Jesus freaks, and DC, spotting a teenage trend that they hadn't exploited yet, hopped on the bandwagon. Here's the cover over of Flash #198 from earlier that year:
Not saying there's anything wrong with religion in comics, but these were extremely rare examples of it anywhere in comics of the Silver Age. Even Christmas covers and Christmas stories which had an honored history in the 1940s were gone.
