Matthew 6:16 says, 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.  Having taught us how to give and how to pray, Jesus now teaches us the correct way to fast.  Since the statement is when we fast, then we can assume that this means we are to fast for spiritual reasons.  I must confess that I never have done this.  My fasting is generally from the time I go to bed until shortly after I get up.  When Jesus speaks of fasting it is fasting done for spiritual purposes, and not for physical ones.  Jesus tells us that we are not to fast to call attention to ourselves as the hypocrites do.  Verse seventeen says, But thou, when thou fastest, anoint thine head, and wash thy face;  Jesus tells us that when we fast that we are to go about life normally, in the way that we look and act.  I believe that what Jesus tells us continually is that the way we live and worship should bring glory to God, and never call attention to our own righteousness.  We are never made righteous by our actions, but can only be made righteous through our faith in Christ as our Savior and Lord.  Verse eighteen states,  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.  We are not to fast for people to notice us, but so they won't.  It may be that they will see us not eating, but even then we are not to call attention to it.  I believe that this is true of any real worship.  We worship so that God will be glorified and we will be edified, and not that we will be praised by people.  When we do, then God will reward us openly.  Even when we proclaim God openly, we are to do it for His glory and not so that we will be praised.  Verse nineteen says, Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal:  I am not sure that God ever expects us to keep all that He blesses us with materially for our own purposes.  Treasures laid up on earth can be destroyed or stolen, and even if they aren't, they will be left behind when Jesus comes again.  Verse twenty advises, But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal:  We lay up treasures in heaven by being obedient to God's will.  Whatever treasures we receive in heaven will be given to us by God and will not be something that we attained by our own ability.  They will still be to be used for God's glory and they will be everlasting. Verse twenty-one declares, For where your treasure is, there will your heart be also.  If we value the things of this world more than following the will of God, then that is what we will devote our time and energy to.  The opposite is also true.  As followers of Christ, we must devote our time and energy into serving God first and foremost.