And He will give you mercy and be merciful to you (Devarim 13:18)
In an extraordinary set of circumstances, the primary component of which is that a Jewish city in Eretz Yisrael should be found to have the majority of its inhabitants guilty of the sin of idol worship, the Torah commands the Jewish people to put the idol worshipers to death by the sword. In addition, the entire city and all of its property — even if owned by those innocent of any transgression — must be totally destroyed. This mound of annihilated property must never be rebuilt; the desolate site must stand as a stark reminder of the inhabitants’ abominable behavior. Then the Torah promises that Hashem “will give you mercy and be merciful to you.” What is the meaning of this promise? Why did Hashem give such a blessing at this point in time?
A human being is a complicated bundle of potential. Under the exterior of every human are traits and powers that remain dormant until acted upon externally. If a person has the inborn nature that leans towards kind deeds done for others, these traits will not activate unless the person does some kind acts prompting new growth in that area of behavior. Unfortunately, the same is true of negative character traits. If one has an inborn cruel nature, one is apt to do cruel things once the power is activated. Therefore, doing cruel things breeds cruelty.
The more one acts in a certain way, the more the corresponding traits will grow. Knowing this, Hashem promises our people that if they adhere to the law and wipe out this city and all of its animals and demolish all its chattels and homes as well, “He will give you mercy and be merciful to you.” Hashem, in effect, will compensate for the lost sensitivity and increased cruelty that must naturally develop due to performance of this mitzvah. “And He will give you mercy.”
Another way of understanding the blessing granted in this verse is based on a Gemara (Shabbat 151b): “Whoever is compassionate towards Hashem’s creatures is shown compassion by Heaven.” Hashem is the ultimate paradigm of kindness. His motivation for creating all that He created was to provide every creation with its needs. Yet, His system requires adherence to justice and truth. Therefore, in spite of the fact that Hashem may want to “give,” the potential recipient of His beneficence may not “deserve” the intended gift — thereby “tying His hands” and preventing delivery of the gift. (Of course, Hashem can do whatever He chooses, but He has set the system within which He runs the Creation to work on justice.) This restriction of Hashem’s power is expressed in the passuk: “One who shuts his ear to the cry of the pauper, he, too, will call out and not be answered” (Mishlei 21:13).
If Hashem wants to do chessed for someone who, in fact, does not deserve it, He provides an opportunity to do a kindness; if the person grabs that chance for chessed, it can tip the scales and make that person worthy of kindness from Above. So often a person is tired or busy when there is a knock at the door. Rather than view it as a stranger annoyingly interrupting, one should consider it as opportunity knocking at the door. It is possibly Hashem providing a test of chessed only to help an individual become deserving of blessing. Listen to the message. Look past the person knocking and see Heaven knocking on your door.