I have spoken concerning this topic many times. The bottom line is that when Jesus says "do not store up treasures on earth where moth or rust destroy but, instead, store up treasures in heaven, for where your treasure is their is your heart" He is calling the Christian to make a decision. This "not storing up treasures" is not a matter of the heart but is a call to not store up wealth in durable goods and money. Money is a form of a durable good like a house in that it can be stored without the value spoiling. This durability is the purpose for money. It is the durability of gold (gold doesn't rust) that led to gold being used as currency. Jesus is clearly playing with the idea of the seeming durability of money in light of more eternal and spiritual, i.e. kingdom, realities.
Many people interpret the passage "for where your treasure is their your heart is also" as saying "for where your heart is there is your treasure also" but that is not what the passage says. It is not where your heart is that determines where your treasure is but where your treasure is that determines where your heart is. If we have treasures on earth then that is where our heart is. If we have durable items stored on earth in the form of money and homes or land, then we must accept that our heart is worldly and carnal and void of the love of God. Therefore, the Christian, the follower of Jesus, is called to make a decision as to whether he or she will seek wealth.
The Problem of Wealth
The human ability to be selfish is manifested in the invention of a means to store up treasures beyond what is natural. This man made means was the invention of currency in the form of durable metals and money. This ability to quantify our wealth in currency has allowed us to "store up treasures on earth". This invention exasperated the problem of inequality. The problem of wealth and unnatural accumulation has been a human problem for a long time. Jesus is not a revolutionary. He is not calling on us to change this reality of the world as it is. Jesus is calling us to live differently and to make a decision.
John Locke was aware of the problem of unnatural accumulation but outside of religion he knew that the state couldn't and shouldn't try to solve this problem. It is just a fact of life that due to the existence of money people can horde wealth. This storing is the primary means that ALL humanity pursues happiness. This storing is ultimately a source of incalculable human suffering. Jesus is calling on Christians through our individual decisions to profoundly impact this most fundamental human problem. the problem of inequality and hoarding. Our response to this teaching of Jesus is central to the mission of the church and the witness of the church.
Jesus is calling the Christian to be different in a real and practical way. We are to make a concrete decision to not store up wealth. This concrete decision to give away our wealth and to refuse to store up money in accounts is the challenge of the passage.
The Decision and the Discipline of Mind
The Christian is called to forsake the accumulation of wealth through his or her labor. This decision is the most counter culture decision of all that the Christian makes. Because this passage is so counter culture and so contrary to all that is around us, precisely because of this affront to our worldview, this passage has been misinterpreted. The Christian must be a critical thinker in order to understand this passage. I have found in life that very few people have the discipline of mind to read the bible for what it actually says especially with respect to Jesus' teachings. The compliant mind assumes that what they have heard from other Christians or from the pulpit is true. This assumption that the church you are in is somewhat correct is the essence of compliant thinking. We must in all things be critical. Because the church is so wrong on this particular issue, we ought to wrestle with this and other hard passages of scripture in the privacy of our own devotional life. This wrestling alone with the text is the essence of being a critical thinker. This takes intellectual courage. What is needed is courageous thinking followed by courageous decisions.
Christians are called to be distinct. We are called to make difficult decisions. These decisions are made not out of fear or compulsion but out of love for God and His ways. We are called to walk by faith. We are called to be courageous. Of all the difficult and courageous decisions we are called to make, I believe this decisions to sell our durable goods and give to the poor is the biggest and hardest decision of all. This decision to empty out our bank accounts and give to the needs of others is a big decision and it is a decision that needs to be made many times over the course of our Christian life. This decision not to save for a retirement of leisure is a big decision, but is there any other way to read Matthew 6? I believe there is not.