Some people have said law and gospel “is just a Lutheran axiom.” Martin Luther was without a doubt one of the most influential spokesman God used to teach the world about the double use of the law in his commentary of Galatians.
However, “when discussing Law and Gospel in connection with systematic or dogmatic theology [John Calvin] is in perfect agreement with Luther’s approach.” Calvin is one of many in the Reformed tradition who is in agreement with Luther.
Zacharius Ursinus, the primary author of the Heidelberg Catechism, states: “The doctrine of the church consists of two parts: the Law and the Gospel; in which we have comprehended the sum and substance of the sacred Scriptures…The law and gospel are the chief and general divisions of Holy Scriptures.”
Additionally, in Louis Berkhof’s “Systematic Theology” he explains this was the norm ever since the Reformation began. “The churches of the Reformation from the very beginning distinguished between the law and the gospel as the two parts of the Word of God as a means of grace.”
This preaching continued from some of the great Puritan preachers like Richard Sibbes, Thomas Cartwright, Thomas Watson, John Owen, and Thomas Goodwin. [The law-gospel distinction] is replete in the sermons and theological treatises of Episcopal Puritans such as Perkins, Richard Sibbes, and Archbishop Ussher; Presbyterian Puritans such as Thomas Cartwright and Thomas Watson; and Independents such as John Owen and Thomas Goodwin.”
In 1884 to 1885, every Friday evening C.F.W. Walther gave lectures on preaching that have now been published and become a classic work for those in Lutheran and Reformed churches. Walther may have said it best, “The true knowledge of the distinction between the Law and the Gospel is not only a glorious light, affording the correct understanding of the entire Holy Scriptures, but without this knowledge Scripture is and remains a sealed book.”
It should be no surprise to hear the importance of law-gospel in the sermons of Charles Spurgeon, “The Prince of Preachers,” who has been regarded as the greatest preacher of all time.“There cannot be a greater difference in the world between two things than there is between law and grace…He who knows the difference, and always recollects it-the essential difference between law and grace-has grasped the marrow of divinity.” 
The list goes on and on, but my point is that if read through some of the church’s greatest theologians and pastors almost all of them talk about how utterly crucial it is not confuse the distinction between the law and the gospel.
 Michael Horton writes about how he has recently been hearing this statement in his article, “The Distinction between Law and Gospel in Reformed Faith and Practice,” 12.
 Michael Horton, “Calvin and the Law-Gospel Hermeneutic,” para. 9, http://web.archive.org/web/20010411225720/http://alliancenet.org/pub/articles/horton.CalvinLG.html.
 Zacharias Ursinus, Commentary of Dr. Zacharias Ursinus on the Heidelberg Catechism (P & R Publishing, 1985), 1-3.
 Louis Berkhof, Systematic Theology (Wm. B. Eerdmans Publishing Company, 1996), 112.
 Michael Horton, “The Distinction between Law and Gospel in Reformed Faith and Practice,” 13.
 C. F. W. Walther, God’s No and God’s Yes: The Proper Distinction Between Law and Gospel (Concordia Publishing House, 1973), 7.
 Quoted by Michael Horton in Horton, “The Distinction between Law and Gospel in Reformed Faith and Practice,” 13.