Training Institutes has the capacity to sustain the process of entry by troops.

We are greatly heartened by the news reaching us of the enthusiastic response of the friends to the Four Year Plan. Particularly encouraging are the efforts of National Spiritual Assemblies everywhere to establish training institutes and to systematically address the development of human resources. The number of national and regional institutes is rapidly increasing, and indications are that there may be more than one hundred operating in the world by the close of the first year of the Plan. We cherish the hope that from each of these centers of learning will issue forth ever-growing contingents of believers capable of carrying out a wide array of services to the Cause, creating thus in every country the capacity to sustain the process of entry by troops.

http://www.bahai.org/library/authoritative-texts/the-universal-house-of-justice/messages/19960806_001/19960806_001.pdf