русский => английский Искусство/Литература Религия Old Church Slavonic

This is from an essay attributed to Peter the Great, addressed to youth to get them to improve their manners (!)
Некоторые советы напрямую касаются пьянства: «…первой не пии, будь воздержан, избегай пьянства, пии, и **яждь** сколько тебе потребно»

I find online: "Репы не яждь," but that doesn't help me. I traced an example to Luke 12:19 (which in English has "eat, drink, and be merry." So does яждь come from есть?
I get that this is Old Church Slavonic, as is in the vocative case (according to some random website), but what does it mean?

Thanks in advance!