To teach a pig to sing

17:19 Feb 3, 2023 

In this example, there is an equivalent expression in English for the Chinese saying, “(赶鸭子上架)driving a duck onto a perch”: It is “teaching a pig to sing.” Both of these sayings describe trying to force someone to do something that they are not capable of doing, something that they feel difficult to do.
U povom slucaju je ipak bolji doslovan prevod, jer bacati bisere pred svinje znaci traciti vreme/znanje na nekoga ko toga nije vredan, a uciti svinju da peva/svira znaci terati nekoga da radi nesto sto je previse tesko za tu osobu, za sta nije sposobna. Hvala svima. Many thanks to all.

16:42 Feb 3, 2023 

се односи на тупавце који нису у стању да разумеју нешто што је изван њиховог разумевања, изван њиховог ограниченог видокруга.

"To teach a pig to sing" се односи на нешто друго: учити слепог да препознаје боје, шепавог да трчи, тј. учити неког нешто што они нису способни да ИКАД науче.

THAT is the relevant context for your text

"people are taught how to profess their faith without being forced to (as if teaching a pig to sing)"

I would understand it as "don't profess your faith to people not capable of understanding what you're talking about" as it would the same as "teaching pigs to sing [= you'll be wasting your time and it annoys them].