Did the sacrified of Jesus is usefull for us?? n what's the reason?

this day i get some religion leasson in my class and then the teacher aks us “Did the sacrified of Jesus long time ago is usefull for us?? and why”
i have no idea about it,,can you help me..
because i think its useless but i cant find the reasons…
sorry if you are not christian but this is for my exams..
thank alot before…
^^v

because i think its useless

Then why should I answer it?