Thornwell on the Westminster Standards
Subscription to the Standards as a protection
We have always heretofore regarded subscription as a security for the sound dispensation of the Word of God. It is for the sake of the people whom the Church wishes trained to wholesome words, even the words of our Lord Jesus Christ, and not simply for the sake of the officers, that she inquires so particularly into their life and doctrine. The things which they profess to believe she requires them to impress upon the faithful.
The Standards as normative in teaching
Hence, our Standards are obviously a guide, a rule, a measure of [the Elders’] teaching. They contain exactly what the Church wants all her children trained to understand and to practise. […] But we do require, and peremptorily require, that all the teachers shall teach only according to this summary, and we do expect that the knowledge in which their hearers are to grow will be precisely the knowledge embraced in these symbols [i.e., confessional standards].
The Standards as the essence of Bible doctrine and morality
That the Catechisms profess to give the substance of the Word of God, as to faith and duty, is obvious on their very face. They reduce the principal instructions of Scripture to these two heads, and then articulately declare what is taught in reference to each; not some of the things, but the very things themselves, and that in their integrity. They omit only those parts of the Bible which do not fall under either of these categories, but there is no hint that they have only selected the principal points pertaining to the topics they have undertaken to expound. They have given the whole essence of Bible doctrine and Bible morality.
Quotations from The Collected Writings of James Henley Thornwell, D.D., LL.D., vol. IV, John B. Adger and John L. Girardeau, editors, Solid Ground Christian Books, 2004 (reprint of Banner of Truth Trust, 1986 edition), p. 368, emphasis added.