The sacrifice for sin was finished

Someone said:
The sacrifice for sin was finished -- paid in full, confirmed by the empty grave. .....

1. If that is so, why does Scripture say?

1 Peter 2:5
Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ.

2. What are these "spiritual sacrifices"?  
3. Who offers them? Do you?
4. When?
5. What are they for?

Sincerely,

De Maria