Good works are required as the means and way for possessing salvation. Even though they don't contribute anything to the acquisition of our salvation, they are necessary to the obtainment of it. No one can be saved without them.
The first part of a good work is the will, the second is vigorous effort in the doing of it. God is the author of both. It is, therefore, robbery from God to arrogate anything to ourselves, either in the will or the act.Institutes, Book 2, Chapter 3
If we can no more bear fruit of ourselves than a vine can bud when rooted up and deprived of moisture, there is no longer any room to ask what the aptitude of our nature is for good.Institutes, Book 2, Chapter 3
When faith be not exercised upon Christ,
it nods and ceases to produce good works. When hope languishes
and becomes inactive, the heart is no longer lifted above the things of
time and sense by a desirous expectation of good things to come.
Then love declines and is no longer engaged in pleasing and
glorifying God. Zeal slumbers and instead of fervour there is
heartless formality in the use of means and performance of duties
But to show our utter destitution, he argues that we merit nothing, because we are created in Christ Jesus unto good works, which God has prepared; again intimating by these words, that all the fruits of good works are originally and immediately from God.Institutes, Book 2, Chapter 3