To call something consequential is to say that it's significant or important, with special attention to the consequences, or effects and outcomes, it brings. The primary meaning of consequential is "following as an effect, result, or outcome." The term ultimately comes from the Latin verb sequī meaning "to follow," which is also the source of the word sequence. A consequential decision is one that will significantly shape what follows. An event that is politically consequential is one that might alter the course of politics in some significant way, and something that proves consequential is revealed over time to have been an important or determining factor in the course of events.
To ensure something is to guarantee or make certain that it will happen. For instance, someone heading to a job interview might leave their house an hour early to ensure that they arrive on time. The verb secure is used with a very similar meaning, but often implies bringing something about, or getting ahold of something. A critically acclaimed book might secure an author's reputation, or an impressive play in a championship game might secure a victory. Additionally, secure is often used to talk about safety, both as a verb and an adjective, e.g. "The townspeople used sandbags to secure the town during the flood; as a result they all felt more secure."
A dilemma is a special type of problem that requires a choice between two equally undesirable alternatives. When faced with a dilemma, we struggle to decide the best course of action. Dilemma comes from the Greek noun dílēmma, meaning "double proposition." In addition to being faced with a dilemma, one can be in a dilemma, or, more precariously, on the horns of a dilemma, meaning that even if you are able to avoid one horn (or choice), you may end up impaled by the other. While we don't often hear of people being trapped by dilemma, we do hear of people being trapped between a rock and a hard place (quite the dilemma!), and the theme of captivity turns up in prisoner's dilemma, a term that is used to talk about the tensions and trade-offs of individuals making decisions in their own self-interest versus for the good of a group.