Question: Why are the Scriptures called Canonical?
Answer: Because the Word is a Rule of Faith, a Canon to direct our lives. The Word is the Judge of controversies, the Rock of Infallibility; that only is to be received for Truth, which is consonant to, and agrees with Scripture, as the transcript with the original. All maxims in divinity are to be brought to the Touchstone of Scripture, as all measures are brought to the standard.
Question: Are the Scriptures a complete Rule?
Answer: The Scripture is a full and perfect Canon, containing in it all thins necessary to salvation: 2 Tim. 3:15, Thou hast from a child known the Holy Scriptures which are able to make thee wise unto salvation. It shews the credenda, what we are to believe, the agenda, what we are to practice. It gives us an exact model of religion and perfectly instructs in the deep things of God. The Papists therefore make themselves guilty, who go to seek out Scripture with their traditions, which they equalize it. The Council of Trent saith, that the traditions of the church of Rome are to be received pari pietatis affectu, with the same devotion that Scripture is to be received with and so bring themselves under the curse, Rev. 22:18, If any man shall add to these things, God shall add unto him the plagues written in this Book.
“Is all Scripture of Divine Inspiration, is it a Book made by GOD himself? Then this reproves, 1. The Papists who take away part of Scripture, and so clip the King of Heaven’s Coin; they expunge the second Commandment out of their catechisms, because it is against images; tis’ usual with them if they meet with anything in the Scripture they dislike, either to put a false gloss upon it, or if that will not do, pretend it is corrupted. These are like Ananias who kept back part of the money, Acts 5:2 so they keep back part of Scripture from the people. This is a high affront to God, to deface and obliterate any part of his Word. By this they bring themselves under that premunire [a writ charging an offense], Rev. 22:19, If any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life. Is all Scripture of Divine Inspiration? 2. It condemns the Antinomians that lay aside the Old Testament as useless and out of date; they call them Old Testament Christians. God hath stamped a Divine Majesty upon both Testaments and till they can shew me were God hath given a repeal to the Old it stands in force. The Two Testaments are the two Wells of Salvation. The Antinomians would stop up one of these Wells, they would dry up one of the Breasts of Scripture. There is much of the Gospel in the Old Testament. The Comforts of the Gospel in the New Testament have their rise from the Old. The great promise of the Messiah is in the Old Testament, A Virgin shall conceive and bear a Son:–Nay, I say more, the Moral Law in some part of it speaks Gospel, I am the Lord thy God; here is the pure wine of the Gospel. The saints great charter where God promiseth to pour clean water on them, and put his spirit within them, is to be found primarily in the Old Testament, Ezek. 36:26. So that they who go to take away the Old Testament, do as Sampson, Pull down the pillars. They would take away the pillars of the Christian comfort. 2. It condemns the Enthusiasts who pretending the Spirit, lay aside the whole Bible, they say the Scripture is a Dead Letter and they live above it. What impudency is this? Till we are above sin we shall not be above Scripture. Let not men talk of the revelation from the Spirit, suspect it to be an imposture. The Spirit of God acts regularly, in works in and by the Word, and he that pretends a new light, which is either above the Word of contrary to it, abuseth both himself and the Spirit. His light is borrowed from him who transforms himself into an Angel of Light. 4. It condemns the slighters of Scripture. Such are they who can go whole weeks and months and never read the Word. They lay it aide as rusty armor. The prefer a play and romance before Scripture, the Magnalia legis are to them minutula. O how many can be looking their faces in a glass all the morning, but their eyes begin to be fore when they look upon a Bible. Heathens die in want of the Scripture and these in the contempt of it. They surely must needs go wrong who slight their Guide. Such as lay the reigns upon the neck of their lusts, and never use the curbing bit of Scripture to check them, are carried to Hell and never stop. 5. It condemns the Abusers of Scripture. 1. Who do mud and poison this pure Chrystal Fountain with their corrupt glosses, who wrest Scripture, 2 Peter 3.16. The Greek word is στρεβλοῦσιν, they set it upon a rack, they give wrong interpretations of it not comparing Scripture with Scripture. The Antinomians pervert that Scripture, Numb. 23:21, He hath noy beheld iniquity in Jacob. Hence, they infer, God’s people may take liberty in sin, because God sees no sin in them. ‘Tis true, God sees not sin in his people with an eye of revenge, but he sees it with an eye of observation. He sees sin not in them, so as to damn them, but he sees it so as to be angry, and severely punish them. Did not David find it so when he cried out of his broken bones? In like manner the Arminians wrest Scripture: John 5:40, Ye will not come to me. Here they bring in free-will. This text shows 1. How willing God is that we should have life. 2. That Sinners may do more than they do; they may improve the talents God has given them, but it doth not prove the power of free-will, for it is contrary to Scripture, John 6:44, No man cometh to me, except the Father which hath sent me draw him. These therefore wring the text so hard as they make the blood come. They do not compare Scripture with Scripture. 2. Who do jest with Scripture. When they are sad they take the Scripture as their lute or minstrel to play with, and so drive away the sad spirit, as that drunkard I have read of, who having drunk his cups, called to some of his fellows, Give us of your oil for our lamps are gone out. In the fear of God take heed of this. Eusebius tells of one who took a piece of Scripture to make a jest of, who was presently struck with frenzy, and run mad. And ‘tis a saying of Luther, Quos Deus vult perdere, etc. whom God intends to destroy, he gives them leave to play with Scripture.
Thomas Watson,1692, A Body of Practical Divinity Consisting of above One Hundred Seventy Six Sermons on the Lesser Catechism Composed by The Reverend Assembly of Divines at Westminster: with a Supplement of some Sermons on several Texts of Scripture (London: Printed for Thomas Parkhurst, at the Bible and Three Crowns in Cheapside, near Mercers-Chappel, 1692), 15, 16-17
 On page 13 Watson writes, “The two Testaments are the two Lips which God hath spoken to us.”