The two focal points of any birthchart are the Ascendant and Midheaven or A and M for short. The Ascendant is the Earth and the Midheaven is Earth's Inner Central Sun. Both bodies, as they relate to the ecliptic, have the most to say about the individual, followed by the luminaries and the rest of the planets. The Ascendant(A) and Midheaven(M) together form the AM principle of the chart. I(the native) AM(the ascendant and midheaven).
A is the first letter of the alphabet corresponding to 1 and Aries(which is the first sign and also starts with an A), the Ascendant is the primary definer of self in the chart. It accurately describes the general looks and mannerisms of the native -more so than any of the other factors. Your Earth, Gaia, or Ascendant sign is the first impression you make and rules your life here on Earth. The Ascendant, by opposition, also rules relationships and social life.
M is the the 13th letter which reduces to 4 and Cancer(the 4th sign/house) and has to do with your mother or roots or foundation. If the Ascendant is your first or nickname, the midheaven is your last or family name. M placed before A gives MA(reverse of AM) which is the common slang for mom or mother. The MC, by opposition, also rules the father, career, and purpose or direction in life.
The Ascendant, as your worldly self, is what you are now, at the physical and mental level, and what you are incorporating into your being until the moment of your death. You have chosen to learn the characteristics of this sign and whatever planets are therein, as necessary components of your current and future self.
The Midheaven, as your heavenly self, is also what you are now, but at the spiritual and soul level, and is what you are expected to contribute to society or the world at large. It gives you access to your entire past history on this planet(akashic record) and the virtues or vices you have acquired, described by the sign or any planets therein. You can tap into these abilities and use them positively or negatively depending on the aspects and your own choice or free will.
The Ascendant and Midheaven also describe the native's conciousness or awareness. With the Ascendant it's more at the mental, social, or even physical level, while with the Midheaven it's more on the feeling level(emotional/spiritual). The Ascendant is lower self or worldly conciouness while the Midheaven is higher self or even Christ conciousness.
When Moses asked God's name and the response was I AM THAT I AM, was there an astrological inference here? Were not the Ten Commandments(ten planets) summarized by two(Asc.and MC). Each of us is a piece of Heaven(Midheaven) and a piece of the Earth(Ascendant), a combination of celestial(MC) and terrestial(ASC), and the A and M of the birth chart summarizes this beautifully and symbolically.