That you appear not unto men to fast, but unto your Father who is in secret: and your Father, who sees in secret, shall reward you openly.
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Glossa Ordinaria
AD 1480
Ap. Anselm: The Lord having taught us what we ought not to do, now proceeds to teach us what we ought to do, saying, “When thou fastest, anoint thy head, and wash thy face.”.
That is, to thy heavenly Father, who is unseen, or who dwells in the heart through faith. He fasts to God who afflicts himself for the love of God, and bestows on others what he denies himself.