Queen Isabella was a devout Catholic. She certainly lived what appeared to be a virtuous and admirable life, at least from outward appearances. Most Christians would find little to criticize about Isabella’s personal conduct. In fact, her behavior was so exemplary that she was awarded sainthood by the Roman Catholic Church in 1874.
Problem is, she had a very bad counselor. Her personal confessor was Tomás de Torquemada, the Grand Inquisitor of the Spanish Inquisition, which Queen Isabella herself created in 1478. Similarly to Queen Isabella, Torquemada also had a very devout and “sinless” lifestyle, at least from outward appearances. However, he believed something most Christians do not presently accept. Effectively, Torquemada believed that torture was justified, if it could prompt a person to confess their sins, repent, and accept Jesus. Once they were effectively in the kingdom, the killing them was doing them a favor. They might backslide after all! The gist of the idea is that it would be far worse for someone to die in sin, and spend eternity in Hell, than be tortured to death in this life, but receive forgiveness and a heavenly reward.
Obviously, the underlying basis for this idea is sin. Without sin, there would be no Hell, no heavenly reward, and so forth.
Torquemada was also one of the most virulent anti-semites in the dark history of Christianity. He orchestrated the forcible expulsion of the Jews from Spain. It would not be overstating the case to say that one of the main reasons that Spain is a poor country today was because of the stupid, blind, and senseless policies of Queen Isabella and Torquemada. By expelling the Jews, Spain decimated the Spanish middle class, where most of the economic activity was being generated. Up to that point, Spain was the superpower. Afterwards, once the economic impact was felt, Spain declined and the British Empire became pre-eminent.
This theology had serious practical for the entire world. A foolish and silly doctrine resulted in the direct death of thousands, and indirectly affected the lives of millions. Thus, what we believe matters. It affects our behavior dramatically.
I still stubbornly maintain that the concept of sin is pernicious and evil. Like I said previously, allowing another person to tell you what is, and is not, in the divine law is a very dangerous thing. Queen Isabella agreed to allow Torquemada to tell her that. He was the one who guided her in her daily life. He fed her the formula for success. And succeed she did! In the context of her culture, Queen Isabella was a superstar. Too bad her delusion had to be so catastrophic for the entire world.
My advice: If you hear a religious leader telling you what is, and is not, sin for you, do not hesitate. Run. Do not walk. Flee.