John Frame has a very helpful and brief (which is also helpful!) essay on the relationship between Law and Gospel. Here is a nice snippet:

The distinction between law and gospel is not a distinction between a false and a true way of salvation. Rather, it is a distinction between two messages, one that supposedly consists exclusively of commands, threats, and therefore terrors, the other that consists exclusively of promises and comforts. Although I believe that we are saved entirely by God’s grace and not by works, I do not believe that there are two entirely different messages of God in Scripture, one exclusively of command (“law”) and the other exclusively of promise (“gospel”). In Scripture itself, commands and promises are typically found together. With God’s promises come commands to repent of sin and believe the promise. The commands, typically, are not merely announcements of judgment, but God’s gracious opportunities to repent of sin and believe in him. As the Psalmist says, “be gracious to me through your law,” Psm. 119:29.