The phrase "his words were a dagger thrust deep into my heart" is a metaphorical expression that describes how someone's words have caused emotional pain or hurt. The phrase suggests that the impact of the words was so strong that it felt like a physical wound as if a sharp dagger had been thrust deep into the speaker's heart. This phrase is often used to describe situations where someone has been deeply hurt by something someone else has said.
Also, the phrase "his words were a dagger thrust deep into my heart" is a figure of speech that uses a metaphor to describe how someone's words have caused emotional pain. The metaphor compares the impact of someone's words to the feeling of being stabbed with a sharp dagger. By saying that the words were a "dagger thrust deep into my heart," the speaker is emphasizing just how much the words have hurt them, and how deeply they have been affected. The phrase is often used to convey a sense of betrayal or emotional distress caused by someone's words.