זעקת סדם ועמרה כי־רבה וחטאתם כי כבדה מאד "The outcry from Sedom an 'Amorah (Sodom and Gemorrah) is great, and their sin has become very serious" (Bereshith 18:20). There appears to be a repetition of the idea in this verse. The holy Ben Ish Hai says in Addereth Eliyahu that the reason for the repetition is that when there is a bitter outcry, it can come for two reasons.
If a person is robbed of a small amount of money, his outcry would not be very great. But if he is robbed daily, so that eventually the amount becomes substantial, then his screams would be very loud. Another example would be if a person was robbed once, but of a substantial amount of money. Even if no other harm befell him, he would still scream out loudly.
In Sedom, both offences were committed. They stole vast amounts of money and did so daily. When the Pasuq says, "The outcry from Sedom an 'Amorah (Sodom and Gemorrah) is great", this refers to the fact that it was done daily. And so that one should not say that the amounts were small, the Torah adds, "their sin has become very serious", to let us know that the amounts were large and thus, they were judged on both accounts.
(See Addereth Eliyahu, Wayyera, 18:20)
Adereth Eliyahu, Addereth Eliyahu, Vayera, Wayera, Parasha of the week, Wayyera