Why do banks provide their credit card for us how can those credit card help their banks?

credit cards are the facility given by the banks for helping customers. by credit card you can perchase any thing with in the limit of credit card. like if u have a credit card of limit 60000 then u can use amount in advance though u don't have money in ur account (but u have to pay the money within 52 day(it vary from bank to bank)).on tht bank offer 1% or higher rate of interest.