What is HKBH trying to teach us by his choice of commandments that make up the Aseret haDibrot
Rashi (Shemos 24:12) writes that the ten commandments are 10 categories which the 613 fall under.The Bamidbar Rabbah writes that there is 620 letters in the ten commandments 613 for the mitzvos and 7 for the rabbanic mitzvos.
It should be noted that singling out asres hadibros is not so simple because we don't want to show that it is more important than any other mitzvah.See gemara Berachos 12 where they tried to insert aseres hadibros into davening.Also standing for aseres hadibros when read is also not so simple see tshuvos HaRambam.
There are many reasons. Gershon pointed out the balance between those for God and those for other people. The Ralbag and R' Saadiah Gaon hold that all other mitzvot can be derived from these ten -- they are, in a sense, "summary" mitzvot. The source for this seems to be Bamidbar Rabbah 13:15. (Thanks to RCW, Alex, and jake for these sources.) Another (this may be more modern) is that they are the foundation of a functional society.
One might also ask why we think there are exactly ten here (besides "tradition", I mean), and why ten is a special number.
I think its clear why the first 8 are part of the Aseres haDibros:
- God's existence - Most fundamental principle of Judaism
- No Idolatry - Worst sin in Judaism
- No false/vain oaths - Once recognize God, must respect His Name
- Sabbath - Testimony to God's creation of Universe.
- Honoring Parents - God and parents are partners in a person's creation.
- 7, 8. Don't Murder, Don't do Adultery, Don't Steal/Kidnap. These are the 3 [worst] categories of sins to other man.
The other 2 are perhaps less expected:
9- Don't do False testimony - This is a way of causing terrible harm without physically doing anything, and involves perversion of justice too.
10- Don't Covet - This affects the person who covets, and may lead to other sins also.
The number ten represents :
the number of fingers on both hands, which, apart from constituting a good mnemonic, also has a deep mystical connotation, in light of man being made in God's image, according to the “Bereshit” parashah of the first book of the Torah;
as well as :
the number of plagues against the Egyptians, which oppressed Israel;
Notice the connection between the first two meanings :
- God, whose Name's initial letter has the value ten, creates man in His image, whose members (hands and feet) have ten fingers each.
Notice also the connection between the last two meanings :
- by ten deadly plagues He chastises Egypt, and by ten life-giving commandments He blesses Israel.
Notice also how the four fingers and one thumb on each hand mirror the inner structure of the ten commandments :
the two hands represent the two tablets;
on each hand, the thumb is set apart from the rest of the four fingers, just as the last commandment in each of the two groups of five commandments is set apart from the first four within the same group.
To better unpack what I meant by the latter remark :
within the first five commandments, the first four are concerned with God, the Heavenly Father of all Creation, whereas the fifth is concerned with our human or earthly fathers and mothers.
within the last five commandments, the first four are concerned with outwardly or physical sins, listed in decreasing order of magnitude, whereas the last one is concerned with inner or spiritual sinfulness.
Then the following chapters, containing the rest of the mitzvot, are nothing else but an unpacking of each commandment from this initial tenfold set of divine laws, relating to them as the seed or root would relate to the rest of the plant. Thus, the sixth reading of the Kedoshim parashah, for instance, is a footnote or commentary to the seventh divine commandment; etc.