Throughout the history of the church, fasting has been seen as a foundational spiritual discipline, but its proper occasion, practice, and meaning have been open to various interpretations. In looking to David in Psalm 35, John Calvin (1509-1564) elaborates from this example a meaning and application of the practice for the church. He argues that in times of necessity and calamity, fasting can serve as a sign of humility and guilt, expressing our response to God’s call for repentance among his people.

Fasting and Signs of Humility

With respect to “sackcloth and fasting,” he used them as helps to prayer. The faithful pray even after their meals and do not observe fasting every day as necessary for prayer or considerWhen God, therefore, calls us to repentance by showing us signs of his displeasure, let us bear in mind that we should not only pray to him in the ordinary manner but also to employ such means as are fitted to promote our humility. it necessary to put on sackcloth whenever they come into the presence of God. But we know that those who lived in ancient times resorted to these exercises when any urgent necessity pressed on them. In the time of public calamity or danger they all put on sackcloth and gave themselves to fasting, so that by humbling themselves before God and acknowledging their guilt, they might appease his wrath. In like manner, when anyone in particular was afflicted, in order to stir himself up to greater earnestness in prayer, he put on sackcloth and engaged in fasting, as being the signs of grief. When David then, as he here tells us, put on sackcloth, it was the same as if he had taken on himself the sins of his enemies, in order to implore from God mercy for them, while they were exerting all their power to accomplish his destruction. Although we may reckon the wearing of sackcloth and sitting in ashes among the number of legal ceremonies, yet the exercise of fasting remains in force among us today as well as in the time of David. When God, therefore, calls us to repentance by showing us signs of his displeasure, let us bear in mind that we should not only pray to him in the ordinary manner but also to employ such means as are fitted to promote our humility. In conclusion, the psalmist says that he behaved and acted toward them as if each of them had been his brother.

Commentary on the Psalms.

Psalms 1-72, ed. Herman J. Selderhuis. Reformation Commentary on Scripture, OT vol. VII, p. 282.