by Dr. Theodore Beza
That which we call The Word of God: Its two parts — the Law and the Gospel: On this subject we call the “Word of God” (for we know well that the Eternal Son of God is also so named) the canonical books of the Old and New Testament; for they proceed from the mouth of God Himself.
We divide this Word into two principal parts or kinds: the one is called the “Law”, the other the “Gospel”. For, all the rest can be gathered under the one or the other of these two headings.
What we call Law (when it is distinguished from Gospel and is taken for one of the two parts of the Word) is a doctrine whose seed is written by nature in our hearts. However, so that we may have a more exact knowledge, it was written by God on two Tables and is briefly comprehended in ten commandments. In these He sets out for us the obedience and perfect righteousness which we owe to His majesty and our neighbors. This on contrasting terms: either perpetual life, if we perfectly keep the Law without omitting a single point, or eternal death, if we do not completely fulfill the contents of each commandment (Deut. 30:15-20; James 2:10).
What we call the Gospel (“Good News”) is a doctrine which is not at all in us by nature, but which is revealed from Heaven (Matt 16:17; John 1:13), and totally surpasses natural knowledge. By it God testifies to us that it is His purpose to save us freely by His only Son (Rom. 3:20-22), provided that, by faith, we embrace Him as our only wisdom, righteousness, sanctification and redemption (1 Cor 1:30). By it, I say, the Lord testifies to us all these things, and even does it in such a manner that at the same time he renews our persons in a powerful way so that we may embrace the benefits which are offered to us (1 Cor 2:4).
The similarities and the differences between the Law and the Gospel: We must pay great attention to these things. For, with good reason, we can say that ignorance of this distinction between Law and Gospel is one of the principle sources of the abuses which corrupted and still corrupt Christianity.
The majority of men, blinded by the just judgment of God, have indeed never seriously considered what curse the Law subjects us to, nor why it has been ordained by God. And, as for the Gospel, they have nearly always thought that it was nothing other than a second Law, more perfect than the first. From this has come the erroneous distinction between precept and advice; there has followed, little by little, the total ruin of the benefit of Jesus Christ.
Now, we must besides consider these things. The Law and the Gospel have in common that they are both from the one true God, always consistent with Himself (Heb. 1:1-2). We must not therefore think that the Gospel abolishes the essence of the Law. On the contrary, the Law establishes the essence of the Gospel (Rom 10:2-4); this is what we shall explain a little further on. For both set before us the same God and the essence of the same righteousness (Rom 3:31), which resides in perfect love to God and our neighbor. But there is a great difference in these points which we shall touch on, and especially concerning the means of obtaining this righteousness.
You can read the rest of Beza's essay Here.