...but what fetters?

Redemption from the curse and bondage of the law is not the retraction of the law's righteous directives. Through the Gospel, the curse of the law’s impossible-to-fulfill demands is removed from us, but the moral law itself remains a lamp to our feet and light to our path, the faithful instruction of a good Master, and a reflection of that holy Christ-like character which we long to attain. Let us not think these things fetters to be thrown off by the advent of the Gospel, but fruits gleaned from Gospel blessings.
John Calvin describes the usefulness of the moral law to the believer in Book II, chapter VII of the Institutes:

“we must be freed from the fetters of the Law, if we would not perish miserably under them. But what fetters? Those of rigid and austere exaction, which remits not one iota of the demand, and leaves no transgression unpunished. To redeem us from this curse, Christ was made a curse for us: for it is written, Cursed is every one that hangeth on a tree (Deut. 21:23, compared with Gal. 3:13, 4:4). In the following chapter, indeed, he says, that “Christ was made under the law, in order that he might redeem those who are under the law;” but the meaning is the same. For he immediately adds, “That we might receive the adoption of sons.” What does this mean? That we might not be, all our lifetime, subject to bondage, having our consciences oppressed with the fear of death. Meanwhile, it must ever remain an indubitable truth, that the Law has lost none of its authority, but must always receive from us the same respect and obedience.”

- John Calvin, Institutes of the Christian Religion II.VII.15