You suggest Mathew 6:19-21 teaches that what we do with our money determines where our heart goes, and when we move our treasure somewhere, our heart follows. I think that interpretation only works if we take the relationship between “treasure” and “heart” as one of causation. I would suggest it’s not necessarily a relationship of causation as much as revelation. What are your thoughts?
It seems clear to me that when Jesus says “where your treasure is, your heart will be also,” he is connecting the two in such a way to indicate they are linked together. Where treasure is placed (on earth or in Heaven), heart will follow. When X is linked to Y, then to move Y is to move X. While it works both ways, in Matthew 6 Christ’s emphasis is on the heart following the treasures. Note he doesn’t say “where your heart is, your treasure will be also.” If he said the latter, would anyone allow us to reverse it and say “what he really means is the former?” No.
Any way we want to phrase it, when you put money in a house, a hobby, a sport, world evangelism, church planting, or feeding the poor, you have invested your heart in it (and I do not believe it is wrong to have the sport or house, this is simply a fact of life). When you give something away, you move your heart away from the bank account or the asset you’ve liquidated, and you move it more deeply into the people you have helped and the Lord you have followed. This is an observable phenomenon, not just one we must accept by faith without understanding how it works. I just think that is the meaning of Christ’s words.