It could be said that practicing the virtues cause growth, but it goes deeper than that. Just practicing the virtues can make us just as legalistic as following the law. For us to truly grow we must take the spirit of the virtues within us. We must look at the meaning and the intent of the virtues. This is more that us taking the virture inside of and saying, for instance, I love people. For us to truly have love in our lives, we must become love. Just as God is love, we also must be love. (This applies to all the virtues .....) What does this mean practically? Let us look at the difference between "having" love and "being" love. When I, as a human, have love within me, it doesn't necessarily mean that love will be within every part of me. I can put love in it's own compartment, ready to be used whenever I so desire. But I can also have hate and jealousy in another compartment, also ready at a moment's notice.
Conversely, when we become love, then there is no room for hate, jealousy, discord, etc. Love spreads to and fills every part of us. There is no longer any room for hate, jealousy, or any other selfish tendencies. Then, when we are love itself, we act in love. We willingly throw out anything within us that hinders the growth of love in our lives. Throughout each day, in our every thought and action, we examine our own thoughts, emotions, and actions. We constantly ask ourselves "Am I acting in love towards myself and others?" One might think that this constant vigilance would be exausting. This would be true if a legalistic or immature mind would try to constantly act in love because it would be against his character. But, when we willingly take love within us to the point that we "become" love, then loving thoughts and actions are expressed easily. It is not tiring at all because it is who we are. Fatigue only comes when we fight against our inner nature. But when our inner nature becomes love, it takes very little effort just to be who we are inside.
This is true of all the virtues. For example, when we become truth (just as God is truth, and we are his children), telling the truth becomes natural to us. We are repulsed at the thought of telling a lie because it is not part of our nature.