Moreover, when you shall fast, be not, like the hypocrites, dejected: for they disfigure their faces, that it may be evident to men that they fast. Verily I say to you, they have their reward. But thou, when thou fastest, anoint thy head, and wash thy face, that it may not appear to men that thou fastest, but to thy Father, who is in secret, and thy Father, who seeth in secret, will reward thee openly.
During the sermon, he shared a quote from John Calvin, which I found most edifying:
Thy Father will reward thee. When he promises a reward from God to fastings, this mode of expression, as we said a little before with respect to prayer, is not strictly accurate. There is a wide difference, indeed, between prayer and fastings. Prayer holds the first rank among the antics of piety: but fasting is a doubtful operation, and does not, like alms, belong to the class of those actions which God requires and approves. It is pleasing to God, only so far as it is directed to another object: and that is, to train us to abstinence, to subdue the lust of the flesh, to excite us to earnestness in prayer, and to testify our repentance, when we are affected by the view of the tribunal of God. The meaning of Christ’s words is: “God will one day show that he was pleased with those good works, which appeared to be lost, because they were concealed from the eyes of men.”