In the Western tradition today along with Friday and Saturday of this week are Ember Days following the Feast of the Holy Cross (Sept. 14). The Ember Days are the Wednesday, Friday and Saturday following the Feast of St. Lucia (Dec. 13), Ash Wednesday, Whitsunday and the Feast of the Holy Cross.
These days have roots in Roman agricultural tradition and were later adapted for use in the Church. There is record of their observance in the Church in Rome in the 5th century. From there the observance spread to England, Gaul, Germany, Spain and beyond. The Eastern Church does not observe these days.
In early tradition the ordination of priests and deacons took place at Easter. In the 5th century, Pope Gelasius permitted such ordinations to also take place on the Saturdays of Ember week.
The Catholic Encyclopedia states, "The purpose of their introduction, besides the general one intended by all prayer and fasting, was to thank God for the gifts of nature, to teach men to make use of them in moderation, and to assist the needy."
Although I am not familiar with the nature of, or to what degree, the observances of Ember Days are practiced today, it is not hard to see that these observances are beneficial reminders of God's mercy in providing for the body. In the Lutheran tradition we repeat, "All this He does only out of fatherly, divine goodness and mercy, without any merit or worthiness in me. For all this it is my duty to thank and praise, serve and obey Him." (SC, Art. I)
And then there are God's abundantly merciful gifts confessed in the Second and Third Articles of the Apostles' Creed . . .