The intercepted letter was conclusive upon a number of points of great interest to Ben-Hur.

It had all the effect of a confession that the writer was a party to the putting-away of the family with murderous intent; that he had sanctioned the plan adopted for the purpose; that he had received a portion of the proceeds of the confiscation, and was yet in enjoyment of his part; that he dreaded the unexpected appearance of what he was pleased to call the chief malefactor, and accepted it as a menace; that he contemplated such further action as would secure him in the future, and was ready to do whatever his accomplice in Caesarea might advise.
And, now that the letter had reached the hand of him really its subject, it was notice of danger to come, as well as a confession of guilt.

So when Ilderim left the tent, Ben-Hur had much to think about, requiring immediate action.

His enemies were as adroit and powerful as any in the East.

If they were afraid of him, he had greater reason to be afraid of them.