Parshas Ekev starts off
וְהָיָה עֵקֶב תִּשְׁמְעוּן אֵת הַמִּשְׁפָּטִים
Rashi says on this:
אם המצות הקלות שאדם דש בעקביו תשמעון:
What is the significance of the so called lite Mitzvos which people trample with there feet?
The Lubavitcher Rebbe writes that the Midrash Tanchuma interprets this verse as saying that this verse refers to mitzvas that people throw under their feet.
The Lubavitcher Rebbe asks what does throwing light Mitzvos have to do with the ankle?
Moreover, it says in Psalms(49:6) that "Why did bad things happen to me? The sin of my ankle surrounds me". The Midrash explains this verse as saying that King David was not worried that he didn't keep the big (important) commandments. He was more worried that he didn't keep the "commandments people throw under their feet". However, there is another verse (19:12) which says "Also your servant guarded them, when he guarded his 'big' heal". ('big' in this context refers to the great reward one gets for the commandments). If so, why was King David worried about the "commandments people throw under their heel".
Therefore, the Midrash means that "worrying about throwing mitzvos under the heel" isn't talking about one who fails to keep the "small" commandment, all the more so it doesn't mean one who embarrasses the commandments (like Rashi's text which refers to the commandments being stepped upon). Rather it refers to a much lighter prohibition.
When one has a choice of how to progress in serving G-d, many times he may think that he has to do so in an orderly progression. First start with the "head" commandments, then proceed down until he reaches the "small" ones. Better, he may say, to first keep the biblical commandments, then the rabbinic, then customs, then one may keep extra "chumras".
One can't begin with "heel" commandments, he claims, before the head commandments. One has to keep Torah and Mitzvos in an order. To keep a stringency before keeping a biblical commandment is like wearing a tie without a shirt, he may claim.
However, even though such reasoning is accurate (even according to "holy intellect", the intellect of Torah), nonetheless, the foundation of all commandments is the "Kabbalas Ol" - acceptance of the yoke. The purpose of a commandment is to connect oneself to Hashem. Therefore, any commandment can accomplish this connection equally, a "big" commandment or a "small" commandment. Whether this mitzvah was written explicitly by the "Great Sanhedrin" or discovered by a modern day Torah Scholar, they are all equal in their effect.
Therefore, King David was worried. Not that he was worried that he didn't keep the "light" commandments. He was just worried that he didn't keep them with the same care as the heavy "head" mitzvos.
It says in the verse in Psalms: "Why did times of evil happen to me? the sin of my heel surrounded me." "In times of evil" refers to behavior (from heaven) that is in a natural way, during the time that Jews are found in exile, as a sheep among seventy wolves, and even (natural) sustenance comes through the supernatural. Therefore, if a Jew thinks (about commandments) in a natural way, which commandment is greater than which, then Hashem looks at him also in a natural way. This results in "days of evil".
However, when one doesn't make such calculations, and one does commandments just to be unified with Hashem, then from above they also treat him in such an unlimited manner.
Therefore, through keeping these "foot" commandments in a happy manner, Hashem gives to the Jews all forms of blessing.
Could it be that the heel is considered a weak point like Achillies' heel? Yaakov held Eisav by the heel trying to hold him back. Perhaps it is a notion of letting our guard down and it will lead to a total lapse of doing mitzvot.
In Sippurei Chassidim (by R' S.Y. Zevin), he brings a story the point of which is that Hashem's desire is that even the person's "heel" - the lowest, crassest, most insensitive part of the body (as the Yiddish expression "Ich her dir mit mayn pyate" - "I hear you with my heel" - i.e., "I am paying absolutely no attention to what you're saying") should be attuned to G-dliness.
The Gemara in Avodah Zara(ב, ב) says that in the Future the gentiles will have a complaint to Hashem we would have accepted the Torah too for the Jews you held Har Sinai over their heads if you would have done it to us we would of also accepted. Hashem hears there complaint and Gives them one LITE Mitzvah the Mitzvah of Sukkah. Hashem takes out the sun and makes it extremely hot they go out and Kick the Sukkah and leave. Now we know why it is all dependant on Lite mitzvah which people trample with their feet as this is the test the gentiles will fail when Mosicach Comes and they have their complaint hence עֵקֶב תִּשְׁמְעוּן the Mitzvah people are דש בעקביו.