Fasting in connection with prayer, penitence, and preparation for new ventures has been practiced from early times in many cultures and religions. The Bible recognizes it as regular in mourning for the dead (1 Sam. 31.13), expressions of penitence (Neh. 9.1), intercession (2 Sam. 12.16), and prayer for God's aid (Judg. 20.26). Fasting was undertaken for personal reasons (Ps. 25.13), as a national act in the face of calamity (Joel 2.15), or as a periodic liturgical observance (Zech. 8.19); normally it involved abstinence from all food to show dependence on God and submission to his will. The great national and liturgical fast was that of the Day of Atonement (Lev. 16.29–34), but fasting was generally recognized, especially after the exile, as a meritorious pious practice and as a potent aid to prayer (Tob. 12.8; Luke 2.37). Later, the author of Isaiah 58 claimed that if fasting was to be of value, it must be accompanied by compassion and a concern for social justice.
Jesus accepted fasting as a natural discipline, and he is described (Matt. 4.2) as deliberately fasting before his temptation and the start of his ministry, similar to the action of Moses (Exod. 24.28). Jesus' disciples, in contrast to the disciples of John the Baptist and those of the Pharisees, appear not to have fasted (Mark 2.18–19): they were in the presence of “the bridegroom,” a parabolic reference to the Messiah, so that fasting was inappropriate. But v. 20 envisages a time of fasting “when the bridegroom is taken away from them”; this verse was probably a creation of the evangelist to justify the church's custom of fasting on Good Friday. Certainly, fasting was regularly observed in early Christianity, and Mark 9.29 (NRSV margin) shows how copyists reflected the commonly held view of the connection between fasting and prayer.
In Acts 9.9, Paul is described as fasting before his baptism, and this became the usual practice from very early times (Didache 7.4; Justin Apol. 1.61; Tertullian Bapt. 20), both for the candidates for baptism and for other members of the church. As baptism was normally celebrated at Easter, this prebaptismal fast was probably the origin of the Lenten fast, which lasted forty days in the time of Cyril of Jerusalem (late fourth century CE), corresponding to the length of Jesus' fast at the start of his ministry.
John N. Suggit