Dallas Willard commenting on Matthew 6:1,
“One of the greatest fallacies of our faith, and actually one of the greatest acts of unbelief, is the thought that our spiritual acts and virtues need to be advertised to be known. ... Secrecy rightly practiced enables us to place our public relations department entirely in the hands of God, who lit our candles so we could be the light of the world, not so we could hide under a bushel. We allow him to decide when our deeds will be known and when our light will be noticed.” The Spirit of the Disciplines (173-74)
Addressing the apparent tension between Matthew 5:16 & Matthew 6:1, A.B. Bruce stated,
“We are to show when tempted to hide and hide when tempted to show."
Jesus is apparently motivating us in Matthew 6 with the promise of reward. Is it selfish or mercenary to be motivated by reward?
No. There is a world of difference between proper and improper rewards, between selfishness and enlightened self-interest. C.S. Lewis wrote with great insight on this point:
“We must not be troubled by unbelievers when they say that this promise of reward makes the Christian life a mercenary affair. There are different kinds of rewards. There is the reward which has no natural connection with the things you do to earn it and is quite foreign to the desires that ought to accompany those things. Money is not the natural reward of love, that is why we call man mercenary if he marries a woman for the sake of her money. But marriage is the proper reward for a real lover, and he is not mercenary for desiring it. A general who fights well in order to get a peerage is mercenary; a general who fights for victory is not, victory being the proper reward of battle as marriage is the proper reward of love. The proper rewards are not simply tacked on to the activity for which they are given, but are the activity itself in consummation.”
I didn't quote this one on Sunday, but Lewis addresses this point again in The Problem of Pain:
"We are afraid that heaven is a bribe, and that if we make it our goal we shall no longer be disinterested. It is not so. Heaven offers nothing that a mercenary soul can desire. It is safe to tell the pure in heart that they shall see God, for only the pure in heart want to. There are rewards that do not sully motives. A man's love for a woman is not mercenary because he wants to marry her, nor his love for poetry mercenary because he wants to read it, nor his love of exercise less disinterested because he wants to run and leap and walk. Love, by its very nature, seeks to enjoy its object."
In Matthew 6:3, why does Jesus say, “Don’t let your left hand know what your right hand is doing?" John Stott offers some insight when he writes,
“Not only are we not to tell other people about our Christian giving; there is a sense in which we are not even to tell ourselves. We are not to be self-conscious in our giving, for our self-consciousness will readily deteriorate into self-righteousness. So subtle is the sinfulness of the heart that it is possible to take deliberate steps to keep our giving secret from men while simultaneously dwelling on it in our own minds in a spirit of self-congratulation.” (Christian Counter-Culture, 130).
Commenting on Matthew 5:5-6, Don Carson writes,
“The person who prays more in public than in private reveals that he is less interested in God’s approval than in human praise. Not piety…but a reputation for piety…is his concern.”
And finally, Matthew 6:16-18 makes clear that we are not to draw attention to our fasting. But what if someone finds out? Is it always wrong to let other people know that you are fasting? John Piper, in his excellent book length treatment of fasting, A Hunger For God, says, “being seen fasting and fasting to be seen are not the same.”