First off, this is the story of David & Goliath. You don't have to be a church mouse to have heard the story of this. the story of the young man and the 9 foot tall beast, and how through trusting in god and showing courage the young David kills the giant with a rock to the head.
Second, This was also one of the first videos in the series, created by animation legends Hanna-Barbera. They're famous for other various toons over the years, including the Flintstones, the Jetsons, Scooby-doo, and the full-length feature Charlotte's Web.
Third, This was also one of famous voice actor Rob Paulsen's first of many roles, before he went on to be really popular with his talents on Animaniacs as Yakko and Dr. Scratchnsniff. He provided the voice of Moki in this series.
Fourth, Blood. I'm not kidding. If this cartoon were made today, the censors would've torn it to shreds before letting it loose. For one, the action sequence at the beginning is quite violent (Goliath and philistines invade a village and some guys get struck down and speared) but the real shock comes near the end after David slings a stone into Goliath's forehead and blood spews out. I remember seeing it as a kid and thinking just how mind-blowing how they showed that. This was a kid's cartoon for crying out loud.
Bottom line, if you happen to swing by a thrift shop and this is available, pick it up, it's totally worth a view. It's often uploaded to Youtube, so you can catch it there too.