The single attribute without which one can not proceed far on the path to spiritual realization is service. Put another way, it is impossible to fully realize one's place in the greater scheme without active service.
This service can come in many fashions. From the prayers of the Hermit to the social activism of the politician. From the nameless service of the unknown to the much publicized and heralded teachings of the sage. The service that is most important; however, is that which is given in the appropriate way, an the appropriate time. That is the truly correct action, which has the potential for the fruit of true benefit to bloom and grow.
Through service one unblocks the dam of selfishness. By putting one's attention on what can be done for another, one opens the door to receiving what is needed for himself or herself. It is not too much to say that service is an indispensable part of spiritual growth.
One only has to look at nature to see the cycle of life. The giving of one part yields the growth of another. It is not until the flower gives of its nectar that its pollen can be carried on. While the process repeats itself in many forms throughout the natural kingdom, it is only when it gets to man that the conscious choice to give reaches its culmination. And here, it is through the appropriate giving of service that it reaches its highest level.
For each person on the spiritual path there is a potential to serve. That is one of the reasons why a neophyte is often given a job to do. By giving, not through greed of receiving something in return, but through right action of service, that person gains in return.
The key here is to focus on what "should" be done in any given situation. If the task is to do the dishes or to dig a hole, to tend the flowers, or to teach a class; then the focus should be upon that, not the result of doing the work - not that others will think more highly or that it satisfies an obligation, not that one feels better for doing so, and not for the creation of a capacity to receive. For all of these limiting actions bring their own fulfillment; and that satisfies any capacity or vacuum in itself. Therefore there is no need or space for a higher, more refined filling to take place.
Thus the first thought in service is what can I do, not what can I get. Then, "what should be done"? Lord, make me an instrument through which all things can come. Show me the way to give, and give me the highest service I may do now - for the best purpose of All. And when one follows that, the means to provide that service will be there as needed. Intention is the key to capacity.