As you might already know, the main business for banks is accepting deposits and granting loans. The more the loans the banks disburse, the more profit they make. Also, banks do not have a lot of their own money to give as loans. They depend on customer deposits to generate funds for granting loans to other customers. So a deposit mobilization scheme would encourage customers to deposit more cash with the bank and this money in turn will be used by the bank to disburse more loans and generate additional revenue for themselves.
The role of the marketing department here is to reach out to more and more customers and explain to them the benefits of depositing their money with the bank thereby generating more deposits for the bank.