II. The foes of the earthly, which are powerless against the heavenly.
The imagery implies a comparatively simple state of society and primitive treasures. Moths gnaw rich garments. Rust, or more properly corruption, would get into a man's barns and vineyards, hay-crops and fruits. Thieves would steal the hoard that he had laid by, for want of better investment. Or to generalise, corruption, the natural process of wearing away, natural enemies proper to each kind of possession, human agency which takes away all external possessions--these multifarious agents co-operate to render impossible the permanent possession of any 'treasure on earth.'
On the other hand, what a man has laid up in heaven, and what he is partially here, have no tendency to grow old. Men never weary of God, never find Him failing, never exhaust truth, never drink the love of God to the dregs, never find purity palling upon the taste, 'Age cannot wither, nor custom stale, "their" infinite variety.'
'Treasure in heaven' has no enemies which destroy it. Every earthly possession has its own foes, every earthly joy has its own destructive opposite; but nothing touches this treasure in heaven.
It has nothing to fear from men. Nobody can take it out of a man's soul but himself. The inmost circle of our life is inviolable. It is incorruptible and undefiled and fadeth not away, for it all comes from the eternal God and our eternal union to Him. He is our portion for ever.
III. The madness of fastening the heart down to earth.
The heart must be in heaven in order to find its true home. It is unnatural, contrary to the constitution of the 'heart' that it should be fettered to earth.
If it is, it will be restless and unsatisfied.
If it is, it will be at the mercy of all these enemies.
If it is, what will happen when the man is no longer on earth? 'What shall it profit a man if he gain the whole world and lose his own soul?'