Faith has an object, and the facts of that object (Christ) can be known and asserted as true and defendable. The promises of Christ are what is yet unseen. So faith rests upon Christ who is trustworthy and able to produce what He has promised as evidenced in scripture. So faith can have a certain and objectively true knowledge of Christ, a personal assent to all that Christ said and promised is true, and rest in the knowledge that the promises will come to pass.
Kind of like a world renowned doctor who comforts a patient that he is able to perform the surgery he needs. The objective facts of his reputation and history of successful operations, makes the promise of coming through this surgery, personal and real to the patient. It is still faith, because the operation is not over yet.