62-3. It should be left to the judgment and discretion of every Christian and family to determine when it is proper to observe a private fast or thanksgiving; and to the church Sessions to determine for particular congregations; and to the Presbyteries, to determine for larger districts. When it is deemed expedient that a fast or thanksgiving should be general, the call for it should be issued by the General Assembly. If at any time the civil power should appoint a fast or thanksgiving, in keeping with the Christian faith, it is the duty of the ministers and people of our communion to pay all due respect to it.

DIGEST: The current text remains unchanged from PCA 1975, noting that with that change in 1975 that we no longer affirm that we live in under a Christian government. Otherwise, the wording of this paragraph is basically that of PCUS 1894.

BACKGROUND AND COMPARISON :
1. PCA 1973, Adopted text, DfW 16-3 (M1GA, Appendix, p. 161)
2. Continuing Presbyterian Church 1973, Proposed BCO text, p. 76
3. PCUS 1933, XVI, §375.
4. PCUS 1929, XVI, §375.
It should be left to the judgment and discretion of every Christian and family to determine when it is proper to observe a private fast or thanksgiving; and to the church Sessions to determine for particular congregations; and to the Presbyteries, or Synods to determine for larger districts. When it is deemed expedient that a fast or thanksgiving should be general, the call for it should be issued by the General Assembly. If at any time the civil power should appoint a fast or thanksgiving, as we live under a Christian government, it is the duty of the ministers and people of our communion to pay all due respect to it.

1. PCUS 1927, XV-4, §369
2. PCUS 1894, XV-4
It must be left to the judgment and discretion of every Christian and family to determine when it is proper to observe a private fast or thanksgiving; and to the church sessions to determine for particular congregations, and to the presbyteries or synods to determine for larger districts. When it is deemed expedient that a fast or thanksgiving should be general, the call for them must be judged of by the General Assembly. And if at any time the civil power should think it proper to appoint a fast or thanksgiving, it is the duty of the ministers and people of our communion, as we live under a Christian government, to pay all due respect to the same.

COMMENTARY:
Morton H. Smith, Commentary on the Book of Church Order, 6th edition, 2007, p. 453-454.
The individual believer may have occasions for either fasting or thanksgiving. In observing such as individual there is no need for outward show, but rather should be done privately unto the Lord, who sees all things.
A family may well want to fast before a major decision. Again, this is something done within the confines of the family, and not for public display. The family may well have occasions for thanksgiving to the Lord for his manifold blessings. This could be done in appropriate prayers of thanksgiving and the singing together of suitable psalms or hymns.
A congregation may be called by the Session to s season of fasting over some matter of special concern or need. It would be appropriate to end the period of fasting with a congregational worship service. In response to blessings from the Lord, it would be most desirable for the congregation to join in a service of thanksgiving to the Lord. Psalms such as Ps. 100 call us to enter his courts with praise and thanksgiving. A presbytery could call for its member churches to observe either a fast or a time of thanksgiving. On such occasions individual services could be scheduled in individual congregations, or joint services would be suitable.
Finally, the whole Church may be called to fast or to enter into thanksgiving. This would ordinarily be done by the General Assembly setting particular times for such. In carrying out such, individual presbyteries and or congregations could set particular services. This paragraph indicates that either ecclesiastical or civil authorities may call for times of thanksgiving or fasting. In either case ministers and the people ought to respond accordingly.