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As to the sufficiency of Scripture, the Bible as a whole, written over centuries by a phalanx of authors, testifies to its own sufficiency in its completeness and excellency through its wisdom, prophecy, and fulfillment, which could in no wise have come from the mind of man, but from God. It needs no external support nor the approval of man.

That's just silly. The Bible nowhere testifies to its own sufficiency, nor completeness. It doesn't even list its own contents.

I think it’s all there, and the martyr who authored the Belgic Confession seemed to think so too:

Article 7: The Sufficiency of Scripture

* We believe that this Holy Scripture contains the will of God completely and that everything one must believe to be saved is sufficiently taught in it. For since the entire manner of service which God requires of us is described in it at great length, no one— even an apostle or an angel from heaven, as Paul says—^2 ought to teach other than what the Holy Scriptures have already taught us. For since it is forbidden to add to or subtract from the Word of God,^3 this plainly demonstrates that the teaching is perfect and complete in all respects.

Therefore we must not consider human writings— no matter how holy their authors may have been— equal to the divine writings; nor may we put custom, nor the majority, nor age, nor the passage of time or persons, nor councils, decrees, or official decisions above the truth of God, for truth is above everything else.

For all human beings are liars by nature and more vain than vanity itself.

Therefore we reject with all our hearts everything that does not agree with this infallible rule, as we are taught to do by the apostles when they say, “Test the spirits to see if they are of God,”^4 and also, “If anyone comes to you and does not bring this teaching, do not receive him into your house.”^5 ^2 Gal. 1:8 ^3 Deut. 12:32; Rev. 22:18-19 ^4 1 John 4:1 ^5 2 John 10

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