Job's friends sit with him in silence—a wise expression of sympathy that was more common in the ancient Near East than in modern Western culture. Later Job will wish that his friends had only remained silent instead of speaking (Job 3:5, Job 3:13). We can learn from this that words are not always necessary (or appropriate) when visiting someone who has suffered a grievous loss.
However, in the case of Job’s friends, even their silence is an indication of the harsh judgments that are busy forming in their minds. In their theology, the only reason why Job could suffer so much is because he did something wrong. That is why they have no words of comfort to give to Job, such as the words we find in Psalm 34:18: The Lord is close to the brokenhearted and saves those who are crushed in spirit.
After seven days, it is Job himself who must break the suffocating silence.
13 And they sat with him on the ground seven days and seven nights, and no one spoke a word to him, for they saw that his suffering was very great.