。
It's our duty to obey the law.
Literal
Law [dat-に] obey [nominalizer-の] [topic-は] our [possessive-の] duty-[assertion-だ]
法 (formal/literary) is used here in place of the casual 法律, without changing the grammar. A small register-only contrast that learners can feel by swapping the words in 法律に従うのは…/法に従うのは… and noting the slight gravitas 法 adds.