How do we know that salvation is a work of the heart according to this parable?

The parable of the tares and wheat teaches that true salvation is a transformation that occurs within the heart, rather than a mere external change. The wheat represents those who have been born again through Christ, possessing a new nature, while the tares symbolize those who remain in their fallen condition. The inability to discern the difference between the two shows that salvation's essence lies in a personal relationship with Christ, not simply in outward actions or professions. God is the only one equipped to search the heart and confirm true salvation, affirming that the essence of faith is deeply rooted in His grace.