Learn Spanish (Latin America): Para defender el espíritu, uno no necesita atacar. - To defend the spirit, one does not need to attack.

Uno is used here as an impersonal subject, meaning 'one' or 'people in general.' Unlike pronouns like yo or tú, which are easily understood from the verb ending, we need to keep uno so the listener knows we mean 'one in general' rather than 'he' or 'she' (since él and ella also use the 3rd person singular form necesita).

If a woman is speaking, should she say una no necesita atacar?

Yes! When using this impersonal structure to talk about a general experience that includes yourself, you can match the pronoun to your own gender. A male speaker says uno, and a female speaker often says una.

Why is defender left in the infinitive after para?

When you want to say 'in order to do something,' you use para followed directly by an infinitive verb (the dictionary form). Because the person defending is the same as the person attacking (the general uno), there is no change of subject, so we do not conjugate defender.

Why do we say el espíritu instead of just espíritu?