What is the meaning of Matthew 6:21?

I begin to see truth in the Bible I never noticed before. Those old fellows got wise to the game. Lay not up treasures on earth—I am short on the quotation, but you recall the idea. The treasures were to be laid up over here where they had some true value.

Lay not up for yourselves treasures upon earth where moth and rust doth corrupt and where thieves break through and steal, but lay up for yourselves treasures in heaven where neither moth nor rust doth corrupt, and where thieves do not break through nor steal, for where your treasure is, there will your heart be, also.

—Matthew 6:19-21, King James Version