“The Law and The Gospel” is a beautiful poem by the Scottish Divine Ralph Erskine (1685-1752). I have not read anything else he has written, but I found this poem conveys clearly and beautifully the proper distinction between the Law and the Gospel.

The law supposing I have all, Does ever for perfection call;
The gospel suits my total want, And all the law can seek does grant.
The law could promise life to me, If my obedience perfect be;
But grace does promise life upon My Lord’s obedience alone.
The law says, Do, and life you’ll win; But grace says, Live, for all is done;
The former cannot ease my grief, The latter yields me full relief.
The law will not abate a mite, The gospel all the sum will quit;
There God in thret’nings is array’d, But here in promises display’d.
The law excludes not boasting vain, But rather feeds it to my bane;
But gospel grace allows no boasts, Save in the King, the Lord of Hosts.
The law brings terror to molest, the gospel gives the weary rest,
The one does flags of death display, The other shows the living way.
The law’s a house of bondage sore, The gospel opens prison doors;
The first me hamer’d in its net, The last at freedom kindly set.
An angry God the law reveal’d The gospel shows him reconciled;
By that I know he was displeased, By this I see his wrath appeased.
The Law still shows a fiery face, The gospel shows a throne of grace;
There justice rides alone in state, but here she takes the mercy-seat.
Lo! in the law Jehovah dwells, But Jesus is conceal’d;
Whereas the gospel’s nothing else But Jesus Christ reveal’d