That's exactly my point though. I'm an atheist, and I don't do good things out of a desire for "rewards in heaven", or rewards of any kind. I don't refrain from stealing because I'm afraid of hell or punishment. As you point out, they're done for the act itself.
This passage presents altruism as a tit-for-tat deal with God. Do good, and you'll get some of that back...later. I promise! It's almost tacky.
It is not about tit-for-tat, it is about trust.
A good parent often wants to give a child something they know will please the child more than what he/she is currently experiencing. Often the child will be angry and scream and hold onto the old, but the parent knows that as soon as the child let go and embrace what the parent has prepared the child will be happy and joyful.
God is more loving that any good parent: God IS Love, 1 John 4:8. I trust God's goodness and follow Him, I therefore don't have any reason to go into a tit-for-tat deal with God.
> This passage presents altruism as a tit-for-tat deal with God. Do good, and you'll get some of that back...later. I promise! It's almost tacky.
Correction: the passage makes no mention of "heaven."
I don't think you mean to say "tit-for-tat" as that means something else, but I do get the gist: it seems that there's some kind of contractual obligation on the part of God. The logical argument being: if you do [GIVE], then He does [REWARD]. This is a subtle argument, but flawed for a number of reasons (and why texts should never be taken out of context).
First, God isn't beholden to anyone. He does as He pleases, and the only "laws" He is bound by is His own nature (good, omniscient, eternal, etc.). There's many examples where Pharisees try to play these logical gotcha games with Christ, and they're always repudiated.
Secondly, the point of the passage itself is twofold: (1) avoid religious hypocrisy, and (2) avoid materialistic vainglory. Reading into the text deeper than that, brings us to my last point...
Finally, given that Christianity is a theist moral system, it makes sense that the ultimate arbiter of "goodness" is God -- in my opinion, that's why Chist brings up the "reward" -- which, for all intents and purposes, might just be God's approval (who knows what that entails).
This passage presents altruism as a tit-for-tat deal with God. Do good, and you'll get some of that back...later. I promise! It's almost tacky.