But thou, when thou fastest, anoint thine head, and wash thy face.
Once again the Lord is introducing a new practice for Christians. Instead of announcing to everyone that we are abstaining from a certain thing for a period of self-denial, we should do this in private between God and ourselves until our spiritual exercise before God is over. We must never do anything with a spiritual flavor and do it to get recognition or honor by those around. God, who sees in secret, will reward openly - later.