Namu or Nam
Nam is an abbreviation of Namu.

Nam means devotion or direction. At any given moment, you are directing your life a certain way. For example, at work your mind may be consumed by the details of your job. At that moment, your life is directed toward your work. You are thinking about work and taking action on those thoughts.

As we chant Nam myoho renge kyo, we're focusing our minds on the Buddha nature within all life. At the same time, we're dedicating ourselves to that Buddha nature, to each and every being on the planet, and to their enlightenment. In a sense, we're making a determination or a vow for the enlightenment of all beings.

The more powerfully you make this determination, the more it will affect your life. The more it affects your life, the more it will affect the lives of other beings as well. As we change ourselves in this way, we change our destiny as well as the destiny of the other beings affected by us.

Myo refers to the spiritual aspect of life.  Ho refers to the physical or material aspect of life.  Combining them together into a single word represents the interpenetration of the two.  The spiritual aspect and the physical aspect are intertwined with each other. 

A writing or a word or music or an action, everything we see around us in the world, is a spiritual entity in itself which contains a spiritual essence of its own.  When you speak, you imbue your words with your spirit.   Thus, they have a spiritual essence.  Once they pass your lips, they are not you.  They are themselves, a separate entity, a sound wave.  They can, in turn, imbue others, even you, with their spiritual essence. 

This is not unlike your own interaction with others. You are changed as the result of your interaction with others. For instance, a person can change your mind about something, inspire you, or make you angry. These kinds of interactions may at first be superficial, but if they occur over time, they can create a more lasting and significant change in you. You, too, have this same influence over the lives of others. Exchanges between us are both physical and spiritual.

The physical aspect is represented by such things as sound waves, facial expressions, ink or paint on a surface, brain waves and other brain functioning. The spiritual aspect is the unseen aspect of these things. Ink on a piece of paper is more than its physical existence. It represents something to us. It has meaning and therefore a life of its own, an influence of its own over those who can perceive that meaning in some sense or another. This is its spirit.

In the words of Nichiren , “What then does myo signify? It is simply the mysterious nature of our life from moment to moment, which the mind cannot comprehend or words express. When we look into our own mind at any moment, we perceive neither color nor form to verify that it exists. Yet we still cannot say that it does not exist, for many differing thoughts continually occur. The mind cannot be considered either to exist or not to exist. Life is indeed an elusive reality that transcends both the words and concepts of existence and nonexistence, yet exhibits the qualities of both. It is the mystic entity of the Middle Way that is the ultimate reality. Myo is the name given to the mystic nature of life, and ho, to its manifestations.”

Renge

Renge literally means lotus flower, which symbolizes the wonder of this Law.

Because the lotus produces seeds and blooms at the same time, renge represents the simultaneity of cause and effect.  The instant you make a cause, the effect is immediately present deep within your life. 

It's significant that Myoho and Renge are combined in the same phrase.  Myoho referring to the spiritual-physical connection, reminds us that the deepest kind of cause we can make is at the level of the spirit.  Physical reality arises from the spirit.  A change in our spiritual selves results in a change in what we do, in our words and actions, which causes a change in our environment.  Taking a specific action is relatively shallow in comparison to changing who we are at base.  While taking an action might be more immediately evident, changing ourselves has a broader result.  Therefore, the deepest, most lasting kind of cause we can make is to change ourselves.  A change in ourselves might not be evident immediately when it happens, especially to those around us who are not inside of our heads, but we can see the results of it in our choices over time.  The most powerful way to change ourselves is by chanting Nam myoho renge kyo.  Therefore, chanting Nam myoho renge kyo is the most powerful positive cause we can make.

Kyo

Kyo means teaching or sutra. It can also mean sound, vibration or rhythm, since a sutra is a sound emanating from a Buddha. 

It is not the teacher, but the teachings that are the key. We do not worship the person, the Buddha. We revere the correct teachings, which are those that lead people to enlightenment. The teaching we refer to is the heart or intent of the Lotus Sutra, the eternal enlightenment inherent within all life, which is the path to enlightenment for all people.

Kyo is the instruction shared between one Buddha and another. It is the path of development of your own Buddhahood and the Buddhahood of all others. The teachings of kyo are the source, the means, the entrance, and the door for all people to open the enlightened condition of Buddhahood within their own lives. It is a teaching which does not separate the spiritual world from the phenomenal world in which we live. It states that the very sounds of our voices are inextricably linked to the spirituality within us. Our lives are full and complete here, right now. Our lives are not separated by time or space from our spiritual selves.

Kyo refers again back to the interpenetration of the spiritual and the physical.  The teaching of a Buddha is itself a Buddha. Nam myoho renge kyo are the words of a Buddha. That phrase instructs us in the nature of Buddhahood and lead us to our own Buddhahood. Therefore, every time you recite Nam myoho renge kyo, you create Buddha sound waves.

From the words of Nichiren, “If one understands that one’s life is myo, then one also understands that others’ lives are all entities of the Mystic Law. This realization is the mystic kyo, or sutra.”