Mr. Frank offered an invitation to the Van Daans because, Mr. Van Daan helped Mr. Frank when he had just moved to Germany, so Mr. Frank thought it would be like pay back for all the help he received.
Mr.Frank was a logical person.When Franks moved to Germany Van Daan family have helped them a lot to pass such situation.And,they offered them to hiding to pay the cost of help done by them.
