When forming “formal” commands in Spanish, that is, with ‘usted’, you use the same form as the third person singular present subjunctive. For example: ‘Quiero que la silla sea más alta’ = ‘I want the chair to be taller’; ‘Sea más amable, por favor’ = ‘Be kinder, please’. The same form ‘sea’ is used in both cases, but it serves different purposes: the first one expresses a desire, the second one, a command or order.