In 5:18, Jesus says that not the smallest letter or mark will pass from God’s law. He probably refers at least partly to the yod, the smallest letter in the Hebrew alphabet. Later rabbis told the story that when God changed Sarai’s name to Sarah, the yod that was removed complained to God for generations till he reinserted it, this time in Joshua’s name. Some teachers also said that Solomon tried to uproot a yod from the Bible, whereon God announced that a thousand Solomons would be uprooted, but not a single yod. Jewish teachers used illustrations like this to make the point that the law was sacred and one could not regard any part as too small to be worthy of keeping.
When Jesus goes on to say that breaking the least command makes one least in the kingdom whereas keeping it makes one great in the kingdom, a prosaic modern reader might ask, “What happens if you break one and keep another?” But such a question misses the point of this typically Jewish language. Later rabbis decided that the greatest commandment was honoring one’s father and mother, and the least, respecting a mother bird; they reasoned that both merited the same reward, eternal life (based on “life” in Ex. 20:12; Deut. 22:7).
Thus if one broke the least commandment, one would be damned; if one kept it, one would be saved. Yet these same sages recognized that everyone sinned, including themselves. They were not saying that some people never broke any commandments; rather, they were saying that people could not pick and choose among the commandments. One could not say, “I am righteous because I do not kill, even though I have sex with someone I am not married to.” Nor could one say, “I am godly because I do not steal, even though I cheat.” All of God’s commandments are his word, and to cast off any is to deny his right to rule over us, hence to reject him. Thus Jesus was saying in a similarly graphic way, “You cannot disregard even the smallest commandment, or God will hold you accountable.”