This is from the enormous anthology of distich poetry assembled by Barthold Nihus, Epigrammata Disticha, published in 1642; the poem is the fourth-century poet Ausonius.
Gratia, quae tarda est, ingrata est; gratia namque,
Cum fieri properat, gratia grata magis.
The vocabulary is keyed to the DCC Latin Vocabulary list. There is only one word in this poem that is not on the DCC list:
namque: for indeed, truly
cum: with (prep. + abl.); when, since, although (conjunction + subj.)
fīō fierī factus sum: become
grātia -ae f.: favor, influence, gratitude
grātus -a -um: pleasant; grateful
ingrātus -a -um: unpleasant, disagreeable
properō -āre: hasten, speed
qui quae quod: who, which, what / quis quid: who? what? which?
sum, esse, fuī: be, exist
tardus -a -um: slow, sluggish, lingering