When a task or duty is so difficult to perform that doing so feels like a burden, it may be best described as onerous. Onerous comes from the Latin word for "burden," onus, which is used in English with the same meaning. A burden is something that is oppressively heavy, and indeed, when we use the word onerous, we evoke the idea of heaviness: an onerous undertaking is one so riddled or "heavy" with hardships it is difficult to bear. Onerous is also used to describe agreements, contracts, or guidelines that are so bogged down with legal obligations or restrictions, the intended benefits or advantages are outweighed.

There are many types of knowledge, and erudition is one of them. Erudition is a thorough, formal, and profound sort of knowledge obtained by extensive research. The term is often used to discuss knowledge in fields other than those of mathematics and the physical sciences—so you're more likely to encounter it in discussion of philosophy or literature than in discussion of biology. Erudition is not a high-frequency word in English, but when it is used, it's likely to be in a context of glowing appreciation, as something that inspires respect or awe.

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.