What is the central theme of Francis Bacon's essay "Of Followers and Friends"?

Bacon's essay "Of Followers and Friends" (ca. 1610), like all his essays, is designed to guide men to a successful life.  Bacon is not so much concerned with moral goodness in life as he is in practical behavior that leads to success in business and government.

The essay discusses in detail the dangers of collecting "followers," those who may or may not be friends but who latch onto a person for their own gain, not for the benefit of the person to whom they attach themselves.  The most dangerous of these Bacon identifies as 

[those] which follow not upon affection to him with whom they range themselves, but upon discontentment conceived against some other; whereupon commonly ensueth that ill intelligence [that is, understanding] that we many times see between great personages.

In other words, Bacon is warning of followers who align themselves with a person solely because they want to harm a third person.  As Bacon points out, many disagreements among the political class are the result of false information designed to create a disagreement.

Bacon's essay singles out followers such as spies, which he calls "espials," as particularly dangerous because they disclose one's secrets to others.  But, always the practical man, Bacon also notes that such followers are popular because they are efficient and spread gossip.

The most beneficial followers, according to Bacon, are those men--often soldiers who have fought for the person and are therefore loyal and trusted--are those whose primary goals are "to advance virtue and desert in all sorts of persons."  In effect, those followers are best who focus on those things that will advance the good of all the people, not just one class.

Perhaps Bacon's most important warning is to avoid relying on a single person:

To be governed (as we call it) by one is not safe; for it shows softness, and gives a freedom to scandal and disrepresentation.

Last, Bacon advises that the most honorable (and safest) course is "to take advice of some few friends," warning, at the same time, that friendship is rare among equals.

In sum, then, Bacon's essay identifies those followers who are dangerous, those who are useful, but concludes that true friends are the best advisers and followers. 

What motivated Francis Bacon to write "Of Followers and Friends"?

Bacon's essays offer an analytic and practical approach to the problems of living in society with others. Bacon is not so much trying in this essay to impose moral values but to take an empirical approach by classifying different kinds of followers (people who are what we might call subordinates).

With this in mind, Bacon divides "followers" into different classes. Ordinary followers are acceptable because they ask nothing more than approval, recommendations, and protection. Costly subordinates, who are always asking for something more or extra, become a problem and should be culled out. Likewise, factious followers tend to focus on divisions and become followers of a person primarily because they are angry and unhappy with someone else, so they should be discouraged. "Glorious" followers are boastful and tend to cause trouble by talking too much and revealing secrets, while other followers are spies.

The best kind of subordinates to have are those that join you because they discern in you a person who will advance them for honorable reasons. However, in the absence of such virtuous people, mediocre followers are fine—and during corrupt periods, active or energetic followers are most helpful. Bacon also advises people to treat followers equally to avoid trouble and notes that true friends are rare—therefore a person is best to keep their circle of advisors small.