Jesus uses this question, which begins with the words "Do you think that these Galileans were more sinful ... in this way?" (verse 2), to challenge the understanding of the people. "You think that these Galileans were more sinful ... in this way, but they were not. But if you do not repent ... same way" or "Do not think that these Galileans were more sinful ... in this way. If you do not repent ... same way" (See: [[rc://en/ta/man/translate/figs-rquestion]])
Here "I tell you" emphasizes "no." Alternate translation: "They certainly were not more sinful" or "You are wrong to think that their suffering proves that they were more sinful"