Chapter 6:16-24 Fasting; The True Treasure; Wealth (Mammon)

6:16 Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward.
When ye fast - A fast is termed by the Greeks νηϚις, from νη not, and εσθειν to eat; hence fast means, a total abstinence from food for a certain time.
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, Psalm 35:13; that is the inside of the duty; be not as the hypocrites, the Scribes and Pharisees,
of a sad countenance; who put on very mournful airs, and dismal looks; made wry faces, and distorted countenances; banished all pleasantry and cheerfulness from them, so that they looked quite like other men than they really were; for they disfigure their faces; not by covering them out of sight, by putting a veil over them, as some have thought; but they neglected to wash their faces, and make them clean, as at other times; and not only so, but put ashes upon their heads, and other methods they used: they discolored their faces, or "made" them "black", as the Arabic version reads it; that they might look as if they became so through fasting: and such persons were in great esteem, and thought to be very religious.

6:17 But thou, when thou fastest, anoint thine head, and wash thy face;
Anoint thine head and wash thy face - These were forbidden in the Jewish canon on days of fasting and humiliation; and hypocrites availed themselves of this ordinance, that they might appear to fast. Our Lord, therefore, cautions us against this: as if He had said, Affect nothing - dress in thy ordinary manner, and let the whole of thy deportment prove that thou desirest to recommend my soul to God, and not thy face to men.

6:18 That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.
Thy father which seeth in secret - Let us not be afraid that our hearts can be concealed from God; 

but let us fear lest He perceive them to be more desirous of the praise of men than they are of that glory which comes from Him.

6:19 Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal:

Lay not up for yourselves - Our Lord here makes a transition from religious to common actions, and warns us of another snare, the love of money, as inconsistent with purity of intention as the love of praise. Where moth rust and rust doth corrupt - Where all things are perishable and transient.

6:20 But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal:
But lay up for yourselves treasure in heaven - That is, either be concerned for, and seek after heavenly treasure,

6:21 For where your treasure is, there will your heart be also.
For where your treasure is, there will your heart be also - This seems to be a proverbial expression, and contains in it another reason, dissuading from worldly mindedness; because of the danger the heart is in of being ensnared and ruined thereby.

6:22 The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.
If thy motive be single — if thou hast only one motive, and that a right one — the master one of glorifying God — if thy eye be single.

6:23 But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness!

When a man’s highest motive is himself, what a dark and selfish nature he has; but when his highest motive is his God, what brightness of light will shine upon all.

6:24 No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon.

No man can serve two masters - Whose orders are directly contrary to one another: He will hate the one and love the other - The word hate has the same sense here as it has in many places of Scripture; it merely signifies to love less - so Jacob loved Rachel, but hated Leah; i.e. he loved Leah much less than he loved Rachel. 

God Himself uses it precisely in the same sense: Ye cannot serve God and mammon - ממון mamon is used for money. 

 He who gives his heart to the world robs God of it, 

and, in snatching at the shadow of earthly good, loses substantial and eternal blessedness. How dangerous is it to set our hearts upon riches, seeing it is so easy to make them our God!