Some sins are obvious. Murder is both a sinful act and arises from a sinful motive. After a murder, there’s a dead body and a murderer with a smoking gun. Murder is obviously and thoroughly evil. And the same is true of adultery, theft, false witness, and a host of other sins.
In today’s sermon text, Jesus deals with sins that are much more subtle. Jesus spends a lot of time in the gospels highlighting the sins of the pious. Here He describes the actions as “righteousness,” and He means that. He is not opposed to the practices He describes. Jesus wants us to give alms to the poor, to pray, and to fast. These are good deeds.
But He says that we might be sinning even when we are performing these acts of righteousness. In part, this is a matter of motive. If we perform these actions before men to be seen and admired by them, then we are sinning. Our acts are correct, but our motives are wrong.
He also addresses the manner of our righteousness, not the acts but the mode of our acts. We are not to announce our generosity, but give in secret; we are not to offer long prayers of meaningless repetition, but to pray in a closet; we are not to fast in a way that calls attention to our fasting, but to fast in festive garb.
So, we need to attend not only to what we do, but to why and how we do it, because even our righteousness may be sin. As Pastor Wilson often says, we have to repent of our virtues as well as our vices.