Learn French: C'est l'héritage le plus important, et tu vas en hériter. - It is the most important heritage, and you are going to inherit it.

The verb hériter (to inherit) is followed by the preposition de in French when you inherit something (hériter de quelque chose). Because the sentence effectively means 'you are going to inherit of it', we must use the pronoun en to replace the entire phrase starting with de. If we used le, we would be ignoring the required preposition.

Why is en placed before hériter and not before vas?

In sentences with a conjugated verb and an infinitive (like the near future tense here: vas hériter), object pronouns always go directly in front of the infinitive they belong to. You are inheriting 'it' (en), not going 'it', so en must go right before hériter.

Why is there a le before plus important?

To say 'the most' followed by an adjective in French, you use a definite article (le, la, or les) plus plus. When the adjective comes after the noun, as it usually does, you have to state the article twice: once for the noun (l'héritage) and once for the superlative (le plus important).

Why does the sentence start with C'est instead of Il est?