Matthew Henry Commentary Matthew 6:16-18

"Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may be seen of men to fast. Verily I say unto you, They have received their reward. But thou, when thou fastest, anoint thy head, and wash thy face; that thou be not seen of men to fast, but of thy Father who is in secret: and thy Father, who seeth in secret, shall recompense thee." — Matthew 6:16-18 (ASV)

Religious fasting is a duty required of the disciples of Christ, but it is not so much a duty itself, as a means to dispose us for other duties. Fasting is the humbling of the soul (Psalms 35:13); that is the inside of the duty; let that, therefore, be your principal care, and as for the outside of it, do not desire for it to be seen. God sees in secret, and will reward openly.