Why is it significant that Elizabeth Proctor would not tell the court of her husband’s infidelity?

When the judge asked her if John had turned from her, Elizabeth said that he had not. Without realizing it, Elizabeth had just sealed her husband's fate. John cried out that he had admitted the truth, but the damage was done. His testimony was rejected.

Elizabeth assumed that she was doing good by, ironically, lying to the court. She most probably believed that the accusation of lechery had been brought by Abigail and that she would clear his name if she lied. Furthermore, she wished to present an image of a loyal husband and father who was righteous. She was convinced that presenting the court with this positive image would favor her husband and would exonerate him from any wrongdoing. Therein lies probably the greatest irony, for he had already confessed to having had an illicit affair with Abigail. Ironically, also, is that if she had told the truth, the outcome would have been completely different.