This is the 267th most frequent Chinese word.
必
"必" means "must" or "necessary."
In this sentence, '必' forms part of the word '必须' which means 'must' or 'have to', indicating necessity or requirement.
我们必须努力学习。
We must study hard.
Here, '必' means 'necessarily', as part of '非必', which implies something is not certain or required.
有志者事竟成，成功非必难求。
For those determined, success will follow; achieving it is not necessarily difficult.
In this context, '必' combines to form '必经', meaning 'must pass through' or 'necessary', indicating something inevitable.