Augustine of Hippo

This is why Moses fasted for forty days, and Elijah, and the Mediator himself, our Lord Jesus Christ: because in this time-bound state of ours restraint from bodily attractions and allurements is very necessary. The people also spent forty years wandering in the desert, and forty days of rain produced the flood. The Lord spent forty days after his resurrection with his disciples, to convince them of the reality of his risen body. …

Sermon 51.32 ↗

Maximus of Turin

Fasting these forty days and nights, holy Moses too merited to speak with God, to stand and stay with him and to receive the precepts of the law from his hand. For although this human condition prevented him from seeing God, yet the grace of his fasting drew him into close contact with the Divinity. For to fast frequently is a portion of God's virtues in ourselves, since God himself always fasts. …

Sermon 35.4