How intensely interesting is the Lord’s illustration of the human heart here! The heart is like a treasure store, and the man is like a collector looking for valuable things to store in it. He knows what he likes and recognises it as having value to him.
What good things come out of the heart? Sincere words of thanks and praise to God, words of truth to ourselves acknowledging what we really are, words of kindness and helpfulness to others, words of exhortation and encouragement, words of testimony and words in defence of the gospel. They are true words spoken in a right spirit.
The trouble is that we spoil this work of God. We can remember those who were at one time all for the Lord, but now their speech is fifty percent banality and focused again on self. What happened? They allowed their hearts to be infested again. The old nature is still in us until we put off our mortal bodies, and if we do not set up a watch, it reasserts itself. God puts new desires on us, new understanding, but how quickly the rubbish builds up: envy, desire for personal acclaim, excessive pleasure in passing things, and lust.