Verse 21 ought to be memorized by every Christian, especially pastors and evangelists because it helps to identify our spiritual direction.  Jesus says that the things that we treasure reveal where our heart is.  This is how we can determine the sincerity of pastors, evangelists, and others claiming to represent God.  Are their lives entangled in mansions, luxury cars, and church buildings that cost millions?  If they are, than we can feel pretty certain that their message will not lead us to the same place that Jesus’ teaching takes us.  Too many evangelists have tried to convince us that God rewards them with wealth and prosperity because of their faithfulness.  But Jesus teaches us that this isn’t so.  His teachings make it very clear that true Christians will be persecuted and reviled not because they are wealthy, but because they preach God’s holiness.  Therefore, God does not validate our faith with wealth, but rather with persecution.

What Jesus is saying about the eye and the light of the body is that if we see spiritual things clearly when we have the correct spiritual attitude and because of that our soul will benefit; but if we are blinded by the material things of the world, we will see life from a distorted point of view that reaches deep into our hearts and blinds us from (His) truth.

In the next verse Jesus makes the distinction even more emphatic when he describes trying to mix wealth and spirit as trying to serve two masters. You cannot love both—they are incompatible no matter how hard some try to teach differently.  You cannot serve God and wealth!  One will most certainly turn you against the other.

What then should we do?  First of all, we should not worry about the material world. This includes what we eat or drink or what we wear.  Today it would include what we drive or how big our home is.  Even nature teaches that God takes care of even the birds of the air.  And how can we compare the latest clothing styles to that of the lilies of the field or any other beautiful flower?  They do nothing to add to the spiritual beauty seen in a true believer. 

Because many seek satisfaction in the material world they develop anxiety, which comes from not achieving their material goal.  Such anxiety or worry cannot change anything.  Material things are simply not important to Jesus.  Our true beauty is in our spiritual purity not in how we decorate our bodies.  These are the things that the world worries about.  God knows our needs and they are under his control.  We must not be concerned with such things but be satisfied with what God gives us.  Whatever we have is sufficient.  The bottom line is that this life is not the life that we ought to be concerned about—it is our eternal spiritual life that concerns the faithful believer.

Listen to the beautiful advice that Jesus gives us in verses 33-34:

Matthew 6:33-34 (KJV)
³³But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.
³⁴Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof.”

The only way to grow as a Christian is to learn that we must seek after God’s kingdom and his righteousness above all things.  Don’t get caught up in the anxiety of what will happen to us tomorrow because there is enough evil to be concerned with today.