Ten Booms would consider it important that the people living with them were smart and would not tell on them.
Explanation:
Ten Booms were a family of Germans who were responsible for helping many German Jews to escape the holocaust and they ran their operations from inside the family.
It was important for them to be able to trust the people they were working with as situations they would find themselves in were rather grave and terrible for them if they were found out.
They needed to be assured of the people that stayed with them for their and their guest's safety whom they were helping with the escape.
