"You spat out Shu, you expectorated Tefnut, and you put your arms about them as the arms of a ka, that your ka might be in them."
- Pyramid Texts, addressing Atum
You inherit your ka from your parents. It is the line of the ka-spirit that connects you to your ancestors; this is the spirit of animation that was given you, that you might live.
The symbol for the ka is a pair of outstretched arms, lifted upwards as in praise or - Egyptian perspective in artwork being as it is - outwards as if to take a child into an embrace. Hug your children, the Pyramid Texts suggest, so that they have souls.
Because your ka is the ka of your parents, the ka of their parents, and so on, your treatment of the ka - whether yours or that of your ancestors - affects your entire family line. You have inherited the blessings that were written into your ancestors' souls; you have also inherited the traumas - as abuse perpetrates abuse. Your ability to cleanse and heal yourself so that the wounds your ka has taken do not spread further also cleanses and heals your akhu.
Your ka is the ka of your parents. Their ka is the ka of their parents. All kau, all the myriad, multiply-split multi-generational lines of it, all kau are, eventually, the ka of Atum. If the cosmos is alive, if there are spirits here, if there are gods and if there are people and if there are beasts and plants and if the stones hold wisdom and the rivers flow, it is because of the ka of Atum alive within us. He put His arms about Shu and Tefnut, and His ka was in them; as one became millions, those millions still carried the essence of the ka. Your ka, your life-spirit, is a spark of the life-spirit of Atum; your very being partakes of the being of the Creator, and is divine. So does everything else's.
We offer to the gods with the liturgy "May your ka be fed." We present gifts with "For your ka." It is in the nature of kau to give, and we give so that the ka is replenished, so that there is ever more to give. Every gift, every act of kindness, every investment, every meal, all of these are acts of sustaining the ka. Offerings are made so that the gods may continue to sustain their generosity; this theological principle is called "Do ut des", "I give so that you may give."
As we give to each other, we sustain each other, we build our strength. These gifts mean that our akhu are not limited to bloodline - as if they could be, because all ka is of the Creator - because there are people who have given us much and are not in our linear families. These are our communities, the worlds in which we gift from ka to ka.
The word "ka" certainly looks related to the word "kau". "Kau" means "victuals". What we eat is of one substance with our ka - not just because all things that are animate, which is all things, are of one substance with our ka, but because it is the nature of ka to be of this flow of life-energy. What you eat is not merely calories to drive your motion and nutrients to build your cells but becomes of the same essence as your very soul. But then again, I repeat myself.
The word "ka" is also related to words related to reproduction, fertility, and virility. The ka is sexual - not just because sexuality is needed to bring about the next generation and pass on that ka-spirit unto it - but because sexuality is part of the flow of life-energy, energy-exchange, that is essential to the ka's nature. The health and stability of your sexual energy, whether it flows in ways that are natural and healthy to you, these are part of your ka.
The word "ka" is also related to words dealing with enchantment and magic. That word "heka", notice the second half of it: it means the activation of the ka. (I folk-etymologied this ages ago as "breath of the ka" and was tickled that I was basically right.) When you do ritual or perform other heka, what you are doing is encouraging your ka energy to move, and that motion is what works the change in the world. Heka, the god, may or may not be Shu, first emanation from the Creator: the space into which being may become.