This is the post #26 of the Calvin's Institutes summary series.
The law (of Moses) was given so that people would look to God for mercy and await the Mediator. It was not given so that anyone would attain eternal life by obeying it perfectly.
The law is "abrogated" for the believers only to the extend that its condemnation is removed for them by Christ. Believers are to still learn and obey the law as to learn and obey God. However, the ceremonial law (sacrifices and rites) are not to be repeated, for Christ has fulfilled them. To repeat the ceremonial laws is to distrust what Christ has done once for all.
Three uses of the "moral law":
1) By showing God's righteous standard, convicts people of their sins. This is useful also to break human pride so that they may look towards God's mercy.
2) By instilling the fear of punishment, the outward evils are kept in check to some degree. This ensures that the world is a liveable place even though it is still inflicted with much human evil. This, however, does not eliminate the evil desires within people, as they are only eliminated by regeneration.
3) Those are God's people make good use of the law when they learn God's will by daily meditating on it. This is the principal use of the law.