You are mistaken that the IOR represents the annual expenses/income of the church, or even a large part of it. The IOR is a bank that provides financial service

You are mistaken that the IOR represents the annual expenses/income of the church, or even a large part of it. The IOR is a bank that provides financial services to Catholic institutions, such as religious communities and Vatican offices. When money is held, it's put in very low-risk, liquid investment accounts, such as government bonds. The clients of IOR use it so they can carry out religious and charitable operations worldwide.