It is hard to know what point Deedat is making here because he doesn’t make any comment about this passage. This is certainly an unusual story to our modern ears and the account has led to some misinterpretation which I will not go into here but I will say this much; that preserving the family line was a very important issue for God concerning the Jews. God had laid down laws to preserve the family line and name and this was just one of those methods that God instituted. It is a purely Jewish requirement and not required of us non-Jews (gentiles).