Breakdown of Domina iubet servum opus finire ante cenam.
Questions & Answers about Domina iubet servum opus finire ante cenam.
Iubet is from iubeō, iubēre and is 3rd person singular present active indicative: (she) orders/commands.
So: domina iubet = the mistress orders.
Because servum is the direct object of iubet: the mistress gives the order to/at the slave (Latin expresses this as a direct object).
Also, iubeō commonly uses the pattern accusative + infinitive:
iubet servum finire = she orders the slave to finish.
Latin often reports commands indirectly with iubeō + accusative + infinitive. This is like English orders [someone] to do [something].
Using an imperative would be a direct command addressed to the slave, e.g. = But here the sentence is narrating what she orders, so the infinitive fits.