In the modern Hebrew translation that was published by the Israeli Bible Society in 1976, and revised in 1991 and 1995, the Greek words τῶν ἐντολῶν τῶν ἐλαχίστων…ἐλάχιστος κληθήσεται…μέγας κληθήσεται… (Matt. 5:19) were rendered הַמִּצְווֹת הַקְּטַנּוֹת…קָטוֹן יִקָּרֵא…גָּדוֹל יִקָּרֵא (ha-mitsvot ha-ketanot…katon yikare…gadol yikare…; …the small commandments…small he will be called…big he will be called). It is highly probable, however, that in this context, Jesus is speaking about מִצְווֹת קַלּוֹת (mitsvot kalot; light, or, less serious, commandments) and not about mitsvot ketanot (little, or small, commandments). “Light commandments” is a rabbinic technical term for biblical commandments of lesser importance. The opposite of mitsvot kalot is מִצְווֹת חֲמוּרוֹת (mitsvot khamurot, heavy, or serious, commandments), commandments of greater importance.
It is likewise probable that in Matthew 5:19 Jesus introduced a word-play: he used the adjectives קַל (kal, light) and חָמוּר (hamur, serious) to speak of people. In reference to people, the Hebrew words kal and khamur can have the senses “insignificant, unimportant” and “significant, important,” respectively.
Obviously, a commandment is not absolutely “light” or “serious,” but only so in comparison to other commandments. One commandment was so “light,” however, that it was often noted as such by the sages:
If, along the road, you chance upon a bird’s nest, in any tree or on the ground, with fledglings or eggs and the mother sitting over the fledglings or on the eggs, do not take the mother together with her young. Let the mother go, and take only the young, in order that you may fare well and have a long life (Deut. 22:6-7; JPS).
Here is what the sages said about this “light” commandment:
-  Compare Numbers Rabbah 8:3. ↩