Rabbi Chanena ben Agil asked Rabbi Cheya ben Abba, "Why does the word,
'signifying that it may be well with thee' not occur in the first copy
of the ten commandments (Exod. xx.) as it does in the second?" (Deut.
v.) He replied, "Before thou askest me such a question, first tell me
whether the word occurs in Deuteronomy or not? for I don't know if it
does." The required answer was given by another Rabbi, "The omission of
the word in the first publication of the ten commandments is due to the
foresight of what was to befall the first tables, for if the word good
had been in the tables, and broken withal, then goodness would have
ceased to bless the sons of Israel."
THE TALMUD, _Bava Kama_, fol. 55, col. 1.