When contemplating changing things with magic we always think about the external. One of the things we need to keep in mind though, is an old saying: “Push where you are strong.” Sure... sometimes we find ourselves in a place where a small push from us can cause a huge effect. However, this isn't because our effort was huge, but because the effort changed the balance of a situation in a positive feedback loop, and that loop exhibited large effects. This is like moving a rock so it rolls down a hill. Just like you can't do that at the bottom of the ocean, you can only use a small effort to great effect in certain circumstances.
Martial Arts understands that the closer you are to your “center” the more power you have to act from. This is especially apparent in Aikido where almost all of your actions come from your center and have the effect of shifting the person out of their center and into a whirlwind of kinetic energy. The further from their center they are, the more easily they are to manipulate. The opposite is also true. The further you are out of center, the harder you have to work to change anything.
This concept is true in Magic as well. The closer you are to your center, the more effective your work can be. While this can be interpreted to mean that if you are completely in center you have awesome power (and this is true), it is more commonly effective to recognize that until those awesome confluences of Mind, Body, Spirit and Energy happen, we will be the most effective trying to change things closer to our center.
The cost of projecting power is well documented in multiple areas. My favorite example is the American Armed Forces. It costs us dozens of times as much to feed, shelter, supply, train and care for soldiers overseas as it would to do the same “at home.” This is also true in magic. It is a WHOLE lot easier to protect your body, than it is to protect your house; which is also logarithmically easier than trying to protect a whole city. There are tricks around this, but fundamentally it is important to remember... The closer it is to you, the more easily you can affect it.
In short... it is FAR more effective to change yourself with Magic than try to change circumstances, consequences and/or other people. If you are reading this book it is probably because you were hoping to be able to learn to control the world around you due to what you learn in here. I won't disappoint. However, keep in mind. If you focus on changing the world around you, you will quickly come to the limits of your abilities from which you won't be able to improve much. If though, you choose to focus on changing yourself, you will find that you will become strong, balanced and wise enough to effect incredible change in ways most couldn't dream of.
External Magic is about changing things around us. It is like going out into the world and learning to lift stronger and stronger burdens. There are pretty cool and quick consequences, but they quickly peak. Consistent and persistent work will help you improve, but there are fairly fundamental limits that are heavily due to your personal limitations.
Internal Magic is primarily about changing your perspective. From overcoming childhood traumas to using divination to understand a situation more fully, the consequences of internal magic are like learning to use a lever. A stronger person may be able to pick up a heavy rock, but with a good lever, a weak one can do so even more effectively.
In the end, I recommend that you practice both. Doing both will empower you to be more effective than 99.9% of people in the world.