While the usage of ought to has been declining steadily in the last 300 years, it is still incredibly common. (The linked Ngram shows that it is roughly 1/3 as frequent as the word table today, and table is not at all an obscure word.) The question is when should you use it, and when to use should or must. Why should I use "ought to"?

Understanding the Context

- English Language & Usage Stack Exchange 'Ought' is an archaic spelling of 'aught', which is another old word meaning 'anything' or 'any'. So the meaning is: None of the believers considered that any of the things they owned were theirs. This is born out by more modern translations of the passage. E.g.

Key Insights

All the believers were one in heart and mind. No one claimed that any of their possessions was their own, but they shared everything ... The current use of ought in standard English is a modal auxiliary (as present or future tense, mainly with to and infinitive). Etymonline says ought has been detached from owe since 17c. and provides the etymology of ought as below: Old English ahte "owned, possessed," past tense of agan "to own, possess; owe" (see owe).

Final Thoughts

How did "ought" lose its original usage as the past tense of "owe"? Verbs like ought, should, must, have to express degrees of desirability or probability, neither of which really apply to non-sentient things like branches. Maybe the branches "ought not reach" according to the writer's preconceived notions of whether they were likely to. Or maybe it's a type of plant that can extract soil-based nutrients from far-reaching branches (like weeping willows, I ...