This distich comes from the Iuvenilia of Marcus Antonius Muretus which you can find online at Google Books.
Labor et Quies
Si tibi grata quies, iuvenis ne parce labori;
Dux ad honoratam est homini labor ipse quietem.
The vocabulary is keyed to the DCC Latin Vocabulary list. There are two words in this poem that are not on the DCC list:
honōrātus, -a, -um: respected, honored
quies (quiētis, f.): calm, rest, quiet
ad: to, up to, towards (+acc.)
dux ducis m./f.: leader, general
grātus -a -um: pleasant; grateful
homo hominis m.: human being
ipse ipsa ipsum: him- her- itself
iuvenis -is m.: youth
labor -ōris m.: toil, exertion
nē: lest, that not
parcō parcere pepercī: spare, be sparing of (+ dat.)
sī: if
sum, esse, fuī: be, exist
tū tuī tibi tē: you (sing.)