In Luke 13:4-5, we read:

4      Or those eighteen, upon whom the tower in Siloam fell, and slew them, think ye that they were sinners above all men that dwelt in Jerusalem?

5      I tell you, Nay: but, except ye repent, ye shall all likewise perish.

In the above passage, the words "sinners," "repent," and "perish" occur in the space of two verses.  For the simple minded, this proximity is all the evidence needed to reinforce the mantra, "Repent of your sins to be saved."

As in Matthew 3:5-9, the underlying Greek word for "repent" is "metanoeo," "to change one's mind."  It will therefore be recalled that the most significant marker to the object of repentance is something in the context that tells you what the subject is said to "believe," or "suppose" or "understand" or "think" or "regard."  This identifies the object of repentance (the belief about which the lost sinner must "change his mind.")

Jesus speaks of a tower in Jerusalem that collapsed and killed 18 people.  The Jewish mind searched for an answer for this tragedy.  They realized that only God can know the secret thoughts and deeds of another man.  Perhaps then, they reasoned, those 18 persons on whom the tower of Siloam fell were actually the 18 worst sinners in all Jerusalem.  God could have gathered them together at the appointed time and place to execute his righteous judgment.  And this is exactly what Jesus says of their faith . . . "Or those eighteen, upon whom the tower in Siloam fell, and slew them, think ye that they were sinners above all men that dwelt in Jerusalem?"