The meaning of this sentence is 'We (must)(should) be clear.' 'We must (let)(make) ourselves be clear.'
The subject is 'We', which is understood to be present. (of course "us" is the object form)
"be" is the verb.
It is the active form. The passive form would be, 'Let us be made clear.'
This is my interpretation. Let us see if there are other ideas.