A rule is a written set of directions to follow. It specifies the activities that we are to engage in for our spiritual development. It is like a plan one receives at a fitness center for building the health of our physical body. The reason we need such a rule is to give us direction, because we are embarking on a path into the future that is unknown to us. Spiritually, we are headed into a territory that is at the moment unknown to us.
Saint Theophan says, the following:
"The rule should be specific: which books to read, when to read them, how much to read, how to prepare to read, how to begin, continue and end the reading, what to do with what has been read. It is the same for prayer, contemplation and other works. We can see that rules encompass all activities and comprise their outer shell like a body. We must apply them with all our powers, all the expressions of our activities so that no action would be taken without the application of its respective rule."
As we begin to adopt an Orthodox Way of Life we are trying to change our way of life. We want to change patterns of behavior. We want to incorporate new priorities and allocate our time in new ways. We want to engage in practices that we have not engaged in before. We want to do it in a way that helps us grow and does not discourage us. Just like in body building, we need a program that builds our strength gradually but consistently.
Saint Theophan advies: "If the beginner has no rule of prayer, he will not know how to pray; and without a rule for fasting, he will not know how to fast. In general, anyone who has no rule will not know how to do anything as he should, and consequently his life will be patterned after his won activities."
A good rule protects us from all the other forces that influence and vie for out attention. The rule is a way to counteract these forces. Saint Theophan says, "A young plant is trellised or tied to a stronger one so that it would stand and grow straight. Anyone who develops himself without a rule is unlearned and untested... when there is no rule, there will inevitably be omissions, mistakes, and pauses."
Your rule should be developed by your efforts, specific to your needs, in conjunction with and approval of your spiritual father.
The path to an Orthodox Way of Life requires certain level of humility. We must see ourselves as weak and poor. We must have a degree of sorrow, contriteness, about our present condition. The first thing Christ said when he began His earthly teaching was, "Repent, for the kingdom of God is at hand!" Repentance must become a central theme of our daily life.
"Therefore we are commanded to repent every day and even every minute. God, be merciful to me a sinner! This should be the ascetics ceaseless prayer."
Reference: Path to Salvation, pp 214-217