There are five kinds of ways that the Kingdom is spread: Gospel presentations, Witness testimonies, Discipleship offers, Kingdom actions, and Divine miracles.We can't determine the fifth, although I've seen plenty of reports of how miracles have been a key part in the spread of the kingdom. Of the other four, there is a clear dividing line between those that can be manufactured in great quantity, and those that can really only be done one-to-one. We are told that someone can be saved if they "confess with their mouth and believe in their heart." The knowledge of what to confess and what to believe can be easily manufactured and distributed on a massive scale. Thus we have ministries from literature distribution to television broadcasting to Internet websites to even megachurch pastoring. We can get a Gospel presentation to most places on the planet, available for the active seeker to find. But this is the equivalent of a Youtube video that tells you how to change the oil in your care, rewrire a light socket, or fix the plumbing under your sink. It's possible to deliver a basic description of why you should do something, what to do, what tools you'll need, the order of the steps, etc. But to get beyond that basic description into really advanced training as an auto mechanic, an electrician or a plumber requires one-on-one teaching, mentoring, apprenticeship, etc. Discipleship offers and Kingdom actions are both significant "limiters" on how fast the Kingdom can spread. To be a follower of Christ seems to require personal interaction with other followers - for fellowship, for the sacraments, for discipleship, for accountability, for joint action. You can't manufacture personal interaction in large quantities like you can a book. It has to be enabled, and people have to want to interact with the newcomers. Yes, it might be possible to be a follower of Christ on a desert island with nothing but, say, a satellite television connection (or, perhaps, hidden away as a secret believer in an apartment in a very closed country, which would not be very different). But while your eternal salvation is undoubtedly secure in such a situation, the fullness of the Kingdom life in the "now" would certainly not be available, and you wouldn't be doing much about some of the commands of Christ (notably, Matthew 28, but also many others). Thus, we ought to be wary of Gospel presentations and Witness testimonies that cannot be linked to Discipleship offers and the possibility of together-Kingdom action. Such presentations and testimonies are not in and of themselves bad - any soul saved ought to be rejoiced over - but at the end of the day conversions based on information without the possibility of relationship are sterile and may be devoid of fruit. This is not the kind of spiritual life that Jesus seems to favor, either in his parables or in his actions toward fig trees. While we should sow the Gospel abundantly, we need to be careful to figure out how to scale the Discipleship offers to the same level.