Matthew 6:17

But thou, when thou fastest, anoint thine head, and wash thy face;

When fasting, keep a normal, cared-for appearance instead of looking disfigured in order to make the fast visible to others. The fast is to be known to God rather than advertised to gain notice or sympathy, with cheerful service to Him instead of a gloomy look that misrepresents Him. This belongs to Christ's plain teaching in the Sermon on the Mount, which opposed the self-righteous practices of the scribes and Pharisees and set forth the far-reaching principles of God's holy law to be received in the heart. It calls for contentment and surrender of the will to the Holy Spirit rather than striving for wealth, place, and honor, working where God assigns in a way He can approve. It also calls for receiving every gift from God with gratitude, ordering life by His word, and diligently studying the Scriptures as the foundation of faith and the assurance of eternal life.

Setting in Sermon

The instruction about grooming normally while fasting rather than displaying signs of fasting belongs to the Sermon on the Mount. That sermon was given especially to the disciples but spoken within hearing of the assembled multitude, and it was delivered on a mountainside after the ordination of the apostles. In it both the disciples and the gathered multitude were taught.

Its teachings are plain and simple, understandable even to the unlearned, serving as a light amid error and a foundation for faith and practice. In that sermon self-righteous teachings and practices of the scribes and Pharisees were opposed, and their misrepresentation of God was corrected. It gives the pure gospel explanation of God's holy law and its far-reaching principles. Those principles must be received in the heart, because the state of the heart shapes the life and character. That explanation sets the holy standard of character, loving God with the whole heart and the neighbor as God requires.

Fasting Without Display

When fasting, the head is to be anointed and the face washed, keeping the usual groomed appearance instead of putting on a disfigured look that makes the fast visible to others. The fast is to be carried on without outward display, with washing and grooming done normally rather than leaving signs of fasting to be seen. A normal, cared-for appearance is to be kept so that the fasting is known to God rather than advertised to others in order to win notice or sympathy.
Service to God is to be cheerful and not gloomy. A sorrowful appearance misrepresents Christ and can make Christians appear abandoned. Secret trials and self-denial are to be entrusted to Christ, while the work of the Spirit in the heart becomes visible in the life.
Fasting and prayer that a person imposes on self in a way that harms health are not required by God. Such harmful exactions can spring from Pharisaical self-righteousness rather than from Christ. Salvation cannot be earned by those works, and sinners must rely on the merits of the crucified and risen Saviour.

Contented Faithful Daily Life

Matthew 6:17 directs the heart and life to contentment and to surrender of the will to the control of the Holy Spirit rather than striving for wealth, status, and room for personal plans. It turns away from strife for place and position, from reaching for honor and recognition, and from elbowing a fellow worker aside to make room for one's own plans. It calls instead to honoring Christ at every step and to desiring most to work in just the place God assigns, where He can look with approval. It calls for recognizing every gift received as coming from God, with gratitude for God's goodness filling the heart so that a heavenly atmosphere surrounds the soul.

It calls for ordering life by the truth of God found in His word, and for diligent study of the Scriptures as the truth of the living God. That truth is the foundation of faith and the assurance on which the hope of eternal life in the kingdom of heaven is built. The explanation of the law given upon the Mount, to which the verse belongs, includes right and holy methods in business transactions and refusing to acquire means unjustly at another's expense. Those who mingle human wisdom with the divine and practice unjust gain show they have not yet learned that law and its explanation, and need a cleansing process, a purging of the soul temple. The lessons in Matthew 6 to which the verse belongs have not yet been learned, and its teaching is to be exemplified in the life.