In any religious organization there are two kinds of growth: planned and accidental.
Planned growth is always preferred because it ensures that the organization has the resources in place to maintain operations and continue to accomplish its primary mission.
The foundations for growth in a religious organization are planning and resources (and maybe a little bit of faith!) During the startup phase, strategic planning will allow you to create growth targets and devise a plan to accomplish them sensibly.
As you execute the strategic plan, your organization can gradually increase its resources to accommodate a steady influx of new participants and followers.
The risk of growing too quickly is that you won't have enough time to scale up your operation; the risk of growing too slowly is that your overhead costs will be disproportionate to your membership.
Rapid growth can also radically change your organization's culture and generate disillusionment among your current supporters. Although religious growth often occurs in spurts, aim for slow and steady growth whenever possible.