be-all and end-all

a be-all and end-all (essential element; supreme issue; entire purpose) — суть, самое главное; смысл, цель

Example 1: Football wasn't a be-all or end-all for him. Jeff was bigger than that.

Example 2: What kind of life do you wish to lead? Is food and comfort the be-all and end-all?

Example 3: The easiest way to monitor change is by weighing regularly. However, weight is not the be-all and end-all and you must keep a check on your general shape and fitness. Lose weight too quickly and you will lose muscle tissue as well as fat.

Example 4: He believes he's the be-all, end-all in politics, but wait until he loses the next election. (=the best, the greatest, his nibs, world beater )

Example 5: Exams are important and necessary, but they can't be the be-all and end-all for our education system.

Example 6: The mentality that standardized testing is the “end-all, be-all” is a “perversion” of what a quality education should be.

the pith and the marrow of smth (=суть, сущность, значение)