A public fast is when, by the authority of the magistrate (Jonah iii.7; 2 Chron. xx.3; Ezra viii.21), either the whole church within his dominion, or some special congregation, whom it concerneth, assemble themselves together, to perform the fore-mentioned duties of humiliation; either for the removing of some public calamity threatened or already inflicted upon them, as the sword, invasion, famine, pestilence, or other fearful sickness (1 Sam. vii.5, 6; Joel ii.15; 2 Chron. xx.; Jonah iii.5; Esth. iv.16;) or else for the obtaining of some public blessing, for the good of the church, -- as to crave the assistance of his Holy Spirit, in the election and ordination of fit and able pastors, &c., or for the trial of truth, and execution of justice, in matters of difficulty and great importance, &c. (Exod. xix.; Acts i.13, 14.)
When any evil is to be removed, the pastors are to lay open to the people, by the evidence of God's word, the sins which were the special causes of that calamity; call upon them to repent, and publish to them the mercies of God in Christ upon their repentance (Joel. i.14; Neh. viii.) The people must hear the voice of God's messengers with hearty sorrow for their sins; earnestly beg pardon in Christ, and promise unfeigned amendment of their life. When any blessing is to be obtained, the pastors must lay open to the people the necessity of that blessing, and the goodness of God who giveth such graces for the good of men. The people must devoutly pray to God for bestowing of that grace, and that be would bless his own means to his own glory, and the good of his church. And when the holy exercise is done, let every Christian have a special care, according to his ability, to remember the poor (Isa. lviii.7, 10; 2 Cor. ix.7; Gal. ii.10.) And whosoever, when just occasion is offered, useth not this holy exercise of fasting, he may justly suspect that his heart never yet felt the power of true Christianity.
So much of fasting: Now followeth the exercise of holy feasting.