This is a poem attributed to Macedonius from the Greek Anthology, rendered into Latin by Hugo Grotius (1583-1645; you can see his edition of the Greek Anthology in Latin at Google Books).
Dulce, Non Triste, Serva
Mens oblita iuvat; iuvat et memor: haec quia servat
Dulce quod est; contra, triste quod illa fugat.
The vocabulary is keyed to the DCC Latin Vocabulary list. There are two words in this poem that are not on the DCC list:
memor (memoris): mindful of, remembering
oblīviscor, oblīviscī, oblītus: forget
contrā: against, opposite (adv. and prep. +acc.)
dulcis -e: sweet
fugō -āre: put to flight
hic haec hoc: this; hōc: on this account
ille illa illud: that
iuvō iuvāre iūvī iūtum: help, assist; please, delight
mēns mentis f.: mind
qui quae quod: who, which, what / quis quid: who? what? which?
servō -āre: save, watch over
sum, esse, fuī: be, exist
tristis -e: sad, solemn, grim