The Westminster Larger Catechism

Q4. How doth it appear that the Scriptures are the Word of God?
A. The Scriptures manifest themselves to be the Word of God, by their majesty[1]
and purity;[2] by the consent of all the parts,[3] and the scope of the whole,
which is to give all glory to God;[4] by their light and power to convince and
convert sinners, to comfort and build up believers unto salvation:[5]
but the Spirit of God bearing witness by and with the Scriptures in the heart of man,
is alone able fully to persuade it that they are the very Word of God.[6]

Proofs
[1] Hosea 8:12; 1 Corinthians 2:6–7, 13; Psalm 119:18, 129;  [2] Psalm 12:6; 119:140;
[3] Acts 10:43; 26:22;  [4] Romans 3:19, 27;  [5] Acts 18:28; Hebrews 4:12; James 1:18;
Psalm 19:7–9; Romans 15:4; Acts 20:32;  [6] John 16:13–14; 1 John 2:20, 27; John 20:31.

Comments

It is important when we consider this catechism question, that we bear in mind what it is not asking. It is not asking: How can we prove that the Scriptures are the Word of God; much less, how can we convince an unbeliever that the Scriptures are the Word of God?

Notice that the fact that Scriptures are the Word of God is not questioned. This question is concerned with how it may be seen that Scriptures are the Word of God, or how our confidence that the Scriptures are the Word of God can be confirmed or strengthened.

There are essentially two parts to the answer. The first part has to do with objective observations which testify of the verity of Scripture; while the second part has to do with subjective testimony with regards to the witness of the Spirit. This second part is actually an acknowledgement,—on the one hand,—that that it is impossible for one to be fully persuaded that the Scriptures are the Word of God without the work of the Holy Spirit in the heart; while, on the hand, an affirmation that the child of God, being indwelt with the Holy Spirit, does not really need any rational arguments to be fully persuaded that the Scriptures are the Word of God. “Ye have an unction from the Holy One, and ye know all things” (1 Jn 2:20), says the Apostle John.

That notwithstanding, the three ways in which “the Scriptures manifest themselves to be the Word of God,” in the first part of our answer, can be helpful to provide material strength to our faith concerning the divine origin of the Scriptures. The first thing that impresses us is the majesty and purity of the content of the Scripture. We need not elaborate on this point, for anyone reading the Scriptures with the aid of the Holy Spirit will not fail to notice the wondrous things contained in it (cf. Ps 119:18, 129). How lofty are the themes, how pure are the expressions! The second thing, which impresses us, is the consent of all the parts, that is to say, its consistency and the absence of contradictions, despite its being written over a long period of time by a number of writers, many of whom never met one another. The serious student of the Scriptures will not fail to notice how they all point to the Lord Jesus Christ. Amazingly, even the historical events experienced by the people of God, that were recorded before the Lord’s birth, point typologically to Him and His work. It is for this reason that the Lord Himself was able to show His disciples how “all the [Old Testament] Scriptures” speaks of Him (Lk 24:27, 44). But thirdly, consider how the Scriptures are often used of the Holy Spirit to cause real and permanent changes in the lives of men. Not only is it true that no other books, in the history of mankind, has a greater impact on society than the Scriptures, but the child of God can testify of how the Scripture convinces, converts, comforts and confirms him in the way of holiness.