est with a genitive and an infinitive means "it is the mark (task, duty) of … to …": adversantis est … succensere "it is the mark of an opponent to be angry".
Pattern: genitive + est + an infinitive or clause as the subject. Supply a noun such as "the mark, the task, the part, the duty": Facultatis rationalis est, considerare "it is the task of the reasoning faculty to consider".
The genitive usually comes first and the infinitive after est. For "my, your" Latin uses the neuter possessive: meum est "it is my duty", tuum est "it is up to you".
A related genitive describes a quality or value: vir magni ingenii "a man of great talent"; amplioris esse criminis "to be (a matter) of greater guilt", that is "to be a graver offence".