27-1. Discipline is the exercise of authority given the Church by the Lord Jesus Christ to instruct and guide its members and to promote its purity and welfare.
The term has two senses:
a. the one referring to the whole government, inspection, training, guardianship and control which the church maintains over its members, its officers and its courts;
b. the other a restricted and technical sense, signifying judicial process.

DIGEST : This is the first chapter of the second section. Section I is the Form of Government. Section II concerns the Rules of Discipline, originally termed the Canons of Discipline in the PCUS drafts of 1867 and 1869.
In the current PCA text, the partition of the second sentence into points a. and b. is a subsequent development. Otherwise, the current text is unchanged from PCA 1973. Both the 1973 and 2003 PCA editions exhibit inconsistency in the capitalization of “Church” in this paragraph. The 1933 PCUS edition is consistent, capitalizing both occurrences. Normally the capitalized form of "Church" should be taken to mean the Church universal or perhaps in some instances the denomination in view; uncapitalized, "church" should imply the local congregation.

BACKGROUND & COMPARISON:
1. PCA 1973, RoD, 1-1, Adopted text, as printed in the Minutes of General Assembly, p. 145
2. Continuing Presbyterian Church 1973, RoD, 1-1, Proposed text, p. 39
3. PCUS 1933, I-§164
4. PCUS 1925, I-§164
Discipline is the exercise of authority given the church by the Lord Jesus Christ to instruct and guide its members and to promote its purity and welfare.
The term has two senses : the one referring to the whole government, inspection, training, guardianship, and control which the Church maintains over its members, its officers, and its courts ; the other a restricted and technical sense, signifying judicial process.

PCUS 1879, I-1
Discipline is the exercise of that authority, and the application of that system of laws which the Lord Jesus Christ has appointed in His Church. The term has two senses, the one referring to the whole government, inspection, training, guardianship, and control, which the Church maintains over its members, its officers, and its courts ; the other a restricted and technical sense, signifying judicial prosecution.

PCUS 1869 draft, I-1
Discipline is the exercise of that authority, and the application of that system of laws, which the Lord Jesus Christ hath appointed in
His Church. The term has two senses, the one wider and more general, referring to the whole government, inspection, training, guardianship and control, which the Church exercises over its members, its officers, or its courts; the other a restricted and technical sense, signifying judicial prosecution.

PCUS 1867 draft, I-1
Discipline is the exercise of that authority, and the application of that system of laws, which the Lord Jesus Christ hath appointed in his church. The term has two senses, the one wider and more general, referring to the whole government, inspection, training, guardianship and control, which the church exercises over its members, its officers, or its courts; the other a restricted and technical sense, signifying judicial prosecution.

PCUSA 1858 draft, Revised Book of Disciplne, I-1
Discipline is the exercise of that authority, and the application of that system of laws, which the Lord Jesus Christ has appointed in his Church. Its ends are the rebuke of offences, the removal of scandal, the vindication of the honour of Christ, the promotion of the purity and general edification of the Church, and the spiritual good of offenders themselves.

OTHER COMPARISONS:
OPC 2005, Book of Discipline, I-1
Ecclesiastical discipline is the exercise of that authority which the Lord Jesus Christ has committed to the visible church for the preservation of its purity, peace, and good order.

COMMENTARY :
F.P. Ramsay, Exposition of the Book of Church Order (1898, pp. 170-171), on I-1 :
The Rules of Discipline
Discipline is such an important function of church courts that a special treatment of it and specific regulations of it are deemed necessary in the Constitution of this Church.
After a chapter of preliminary definitions, and a chapter concerning the discipline of non-communicating members, these Rules contain, first, three chapters on the Principles underlying Judicial Procedure : one treating of Offences ; one of the Censures that may be used upon Offenders ; and one on the Parties in cases of Process. In the second place, there follow Regulations concerning Process. In four chapters are Regulations governing the Conduct of Process : one containing General Provisions ; two containing Special Provisions pertaining to Process before Sessions, and to Process before Presbyteries ; and one on Evidence. Then are two chapters on Administration of Censures ; one on their Infliction, and one on their Removal. And there is appended a chapter on Cases without Process. Following these two parts, the one on Principles and the other on Process in the courts of Original Jurisdiction, comes the third part of the Rules, which defines exactly the Jurisdiction of the various courts, and in which is much matter that might as well have been put in the Form of Government. This part has three chapters : one on appellate jurisdiction ; one on substitutes for carrying an issue to a higher court ; and one on the determination of the jurisdiction to which any given person is subject.
Chapter I. Of Discipline--Its Nature, Subjects, and Ends.
The first paragraph defines discipline ; the second specifies its subjects ; and the other two treat of the ends of discipline, one especially of the ends of the one kind of discipline, and the other of the ends of discipline in general.
143.--I. Discipline is the exercise of that authority, and the application of that system of laws which the Lord Jesus Christ has appointed in His Church. The term has two senses, the one referring to the whole government, inspection, training, guardianship, and control, which the Church maintains over its members, its officers, and its courts ; the other a restricted and technical sense, signifying judicial prosecution.
It is noticeable that technical discipline is simply a means or form of discipline in the larger sense, and that it includes all the parts of judicial prosecution, as well as the infliction and removal of censures.

Charles Hodge, on Chapter 1, paragraph 1 of "The Revised Book of Discipline" (1858), pp. 694.
This chapter has been reduced from seven sections to three, and from forty-three lines, to twenty-three. The design of the chapter is to state, first, The nature of discipline; secondly, Its grounds; and thirdly, Its subjects. The word discipline is used in different senses. It sometimes has the general s ense of training, whether of the mind, heart, or life. In this sense, it includes all instructions, exhortations, admonitions, and directions. Sometimes it means a mode of government, as when we speak of the Methodist discipline. Sometimes the word is taken in the restricted sense of punishment; and a Book of Discipline, when distinguished, as it is with us, from “the Form of Government,” is a book which gives direction for the administration of discipline in the restricted sense of the term. It concerns, not teaching, but the administration of justice, and exercise of authority. It is therefore defined to be, “ the exercise of that authority, and the application of that system of laws which the Lord Jesus Christ hath appointed in his church. Its ends are the rebuke of offences, the removal of scandal, the vindication of the honour of Christ, the promotion of the purity and general edification of the church, and the spiritual good of offenders themselves.” It appears from this, that discipline, as here used, includes the ideas of oversight and punishment.