I think it depended on the relgious beliefs of the pastor, was a "local" ruling :-) It sounds like a "Catholic" sort of cross with Jesus on it; they often have lots of pictures/representations of Jesus on the Cross. Your pastor may have been reacting to that. Or, the Jews were originally told not to make "graven images" -- artwork of what was Holy/God because you can't really represent "God" in all His Glory and God had the trouble with the early Jews of them worshipping whatever they made; the golden calf, etc. Relying on the "symbol" instead of the actual Living God is a no-no and a lot of people get to treating a rosary or necklace or some object like that kind of like a "lucky" charm (St. Christopher medal comes to mind). That the necklace was so valuable, 24k gold, makes it appear too/very "special" in its own right rather than what it's representing and that's going the wrong way.

But it's all according to one's personal beliefs! If I liked the necklace and was not feeling wrong toward it, just liked it as a necklace, etc. I would have continued to wear it (or, if I didn't have the same beliefs as the pastor). No one outside ourselves has the keys/knowledge about our beliefs. Beliefs are 100% personal, non-transferable, etc. The necklace was sacrilegious to the pastor but that doesn't make it sacrilegious to you/your son unless you choose to belief that way. The pastor is not God, can't make any rules, just suggestions and comments on his own beliefs of what is true.