Future consideration
Instead of being completely oriented in the past and present, Malthus urges his reader to consider the direction of trends to predict the future. He sees that if people continue to have babies at the rate they were currently doing so, that eventually, population booms might become out of control. This idea still has a considerable political thrust today, so it is worth considering. Famously, there are counterpoints to this argument, but in any case, the imagery is clearly wise; by considering the risks of the future, a society can hopefully mitigate risks.
Mathematic imagery
The essay quickly turns into a mathematical analysis of population growth. Instead of seeing population growth as an arithmetical function, Malthus correctly analyses population growth as a higher caliber of growth function, the geometric function. This means that term by term (in this case generations would be the term), growth is occurring by way of multiplication instead of addition, because each person has the means to reproduce in a multiplicative manner. This is an important part of understanding Malthus's argument.
Resource scarcity
This imagery starts with a simple concern, and then Malthus fleshes out that concern, elaborating the imagery. The idea at its root is simply this question: "What if population outgrows the resources it needs?" The answer is that such situations would lead to dire straights for the economy and civilization. With such competition, the very fabric of society could change, because people would be forced back into animal modes of competition, including theft and murder, he fears.
Pessimism as a tool
Malthus isn't an optimist, one might say. But that is not necessarily a bad thing. Malthus shows through Essay why it serves someone to be pessimistic. It is a tool for longevity, because life is full of twists and turns, and by considering the worst-case scenario, one can prepare more effectively for bad times. This Essay is famously pessimistic, and the counterpoints to his arguments are the counterpoints of optimism. More people also means more problem solvers, etc. However, his point that pessimism is a useful tool is clearly self-evident.
