But you, when you fast, anoint your head, and wash your face,
That you be not seen of men to fast,
But of your Father who is in secret,
And your Father, who sees in secret, will recompense you.”
So when they fast they are not to put on a sombre face, or to fail to shave or wash their faces, or to anoint their heads with oil (a contemporary Jewish practise), so that men will realise that they are fasting. They must rather wash their faces and anoint their heads, in other words try to give the impression that life is going on as normal so as to avoid being lionised. By doing it this way only God will be aware that they are fasting. And then their Father, Who sees in secret will recompense them, because they are doing it in order to demonstrate their love for Him. The basic point, as previously, is the genuine motive that lies behind their actions. Their hearts must be right towards God.
Note on Fasting.
As mentioned the general approach of Christians towards fasting was to fast on Wednesdays and Fridays. This fast would end around 15:00 hours (the afternoon meal). Ideally the very fact of doing it would turn their thoughts towards God during that day. At other times they would fast because they were engaged in long sessions of prayer. Fasting as an ascetic practise only became involved much later, and was based on a false idea of the sinfulness of the flesh. It drew great honour from men (who always honour what they themselves are not prepared to do) and was thus a dangerous practise, involving the ascetics, many of whom were not truly godly men, although some were, in a similar condemnation to the Pharisees.
People under eighteen should not fast without consulting a doctor for health reasons. And all should seek medical advice before engaging in long fasts. God does not intend us to dishonour Him by harming ourselves physically. We are not even sure what the full basis of a ‘forty day fast' was (wild fruit or other occasional sustenance may have been taken) and it was always in exceptional circumstances and with exceptional people. Thus we must be sensible and careful. There is nothing in Scripture that indicates that fasting as such brings blessing in itself. The blessing comes in respect of the right attitude of heart and circumstances that accompany the fasting.
End of note.