If we only practice compassion on the mind level, we run a great risk of our compassion being just talk. As we know, talk is cheap. To develop true compassion we have to put our money where our mouth is.
Ego's trick is to make us lose sight of our interdependence. That kind of ego-thought gives us a perfect justification to look out only for ourselves. But that is far from the truth. In reality we all depend on each other and we have to help each other. The husband has to help his wife, the wife has to help the husband, the mother has to help her children, and the children are supposed to help the parents too, whether they want to or not.
The more successful you become, the more the demands of your ego will increase. In the beginning, you simply want to succeed, but your ego will not be satisfied. When you become a little more successful your ego wants to kill your competition. And when you become even more successful, it wants to make you the universal king. There's no telling what ego wants because our desire doesn't have any limit; therefore, its demands continually increase.
Training in compassion is a mental activity. but our mind should also be brought to the level where every action we take is influenced by compassion. That means engaging ourselves in compassion in action.