An intense emotional outburst and a storm of inner thoughts drive Zophar to speak out against Job's harsh claims. Deep reflections stir within him, branching out from his heart much like the branches of a tree [רמב״ן]. These racing thoughts are the catalyst for his response, compelling him to address the insults directed at him.
The primary approach among commentators is that these inner reflections provide Zophar with the exact answers he needs to counter Job's arguments and defend against his insults [רש״י, מצודת דוד, רמב״ן, ביאור שטיינזלץ]. However, others suggest these thoughts actually cause Zophar to retreat from his previous stance. This shift might be a turn away from philosophical reasoning back toward relying on basic everyday experience [מלבי״ם]. Alternatively, it could be a retreat from his initial desire to judge Job favorably, a charity he abandons after witnessing Job's current arrogance [אלשיך].
Beneath this reaction lies a deeper motive, which commentators understand in three distinct ways. First, the trigger for his response is actually his prior silence. Because Zophar sat quietly and listened to Job's insults, his thoughts have boiled over, leaving him no choice but to finally speak [רש״י, ביאור שטיינזלץ].
A second perspective focuses on deep feelings and senses. Emotionally, Zophar experiences a profound sense of hurt and shame from Job's words, prompting his reply [מצודת דוד, רלב״ג]. On a more physical level, this reliance on the senses means Zophar is drawing upon his own sight and hearing. He uses his real world observations to prove Job wrong, seeking to show that the wicked inevitably meet their downfall [רמב״ן, מלבי״ם].
Finally, a third approach centers on a feeling of rushing or haste. Zophar may be expressing a sudden urgent need to reply immediately [אבן עזרא]. On the other hand, he might be admitting that his previous arguments were made too quickly and without enough thought, making it necessary for him to speak again to correct his past mistakes [אלשיך].