Learn Italian: Ciò che fa bene allo spirito fa bene all'anima. - What is good for the spirit is good for the soul.

When "what" is not a question but instead means "the thing that" or "that which", Italian uses a compound relative pronoun like ciò che or quello che. You use cosa or che cosa for asking actual questions (like "What are you doing?"). Here, quello che would also work perfectly and mean the exact same thing.

The English translation says "is good", so why do we use fa (from fare, to do/make) instead of è (is)?

In Italian, to say that something "is good for" you (like food, exercise, or an environment), you use the expression fare bene a (literally "to do well to"). Using the verb essere here wouldn't sound natural to an Italian speaker.

Why does the preposition change from allo for the spirit to all' for the soul?

Both use the preposition a (meaning "to" or "for" here) combined with the word's specific definite article. Spirito requires the article lo because it is a masculine word starting with an s plus a consonant, creating allo. Anima starts with a vowel, so its feminine article la drops its last letter to become l', creating all'.

Do I need to repeat a subject before the second fa bene?