Learn Portuguese (Portugal): A pá é essencial para desenterrar os fragmentos. - The shovel is essential to unearth the fragments.

Because the action is general. We are stating a general fact about the shovel's purpose. If you wanted to specify exactly who is doing the unearthing, you would conjugate it into the personal infinitive, such as para desenterrarmos (for us to unearth) or para desenterrarem (for them to unearth).

Since this lesson covers até, could we use até instead of para in this sentence?

It would completely change the meaning. Para indicates purpose (essential in order to unearth). If you used até, it would indicate a temporal limit (essential until unearthing), which does not make logical sense for describing a tool's function.

Why do we need the preposition para before the verb?

In Portuguese, when an infinitive expresses a purpose or objective, meaning "in order to", it must be preceded by para. English often just uses "to" (essential to unearth), which can sometimes trick learners into dropping the Portuguese preposition.

Is there an easy way to remember the meaning of desenterrar?

Yes! It shares the exact same morphological structure as its English translation "unearth". It combines the prefix des- (meaning reversal or removal, like "un-") with the root word terra (earth or dirt) and the verb ending -ar.