What does Mr. Wopsle say about "the prodigal?" Why did Dickens include this allusion?

There is an intense awkwardness and embarrassment during this Christmas day lunch as Mr. Wopsle and Mr. Pumplechook discuss Pip in his presence, with the agreeing voice of his sister and poor ineffectual Joe, who can do nothing to support Pip in his time of need than to pour ever greater quantities of gravy on to his food. Note what Wopsle says:

Win were the companions of the prodigal. The gluttony of Swine is put before us, as an example to the young... What is detestable in a pig, is more detestable in a boy.

Thus the allusion to the Parable of the Prodigal Son is used by Wosple to make a deeply unfair criticism of Pip, by comparing him to the swine in that story and arguing that he is has the same gluttony as the swine, and is therefore deeply evil in the way he reacts to the "love" his sister shows him in bringing him up.

Mr Wopsle is the clerk for the church and he says that 'Swine were the companions of the Prodigal (Jesus)' Mr Wopsle says it to suggest there is something wrong with Pip. Dickens includes it to make a joke about Mr Wopsle eating pork whilst talking about pigs.