Astronomy and astrology were closely linked in the 16th century, and contrary to what many interpreters believe, these verses are a plea for, and not against, astrology. Nostradamus was a doctor-astrologer and he became one of the most famous astrologers of his time:

Close bonds have always existed between and astrology. Indeed, until the 18th century, the two sciences were inextricably mixed, a study of astrology being, as a matter of course, part of a doctor's training and a vital element in his treatment of disease... ...Astrology owed its prosperity in the Renaissance period, in part at least, to the Church and to the positive encouragement it received from several popes....Leo X brought a bevy of astrologers into the papal court to advise him throughout his reign...and Paul III used astrologers to fix the hours for his Consistory. [The Compleat Astrologer - Derek and Julia Parker]

Latin being of common use in those days, and Nostradamus being a physician-astrologer, the present quatrain is, in a way, a kind of 'prescription' against stupid critics. Each latin word is important, and I therefore translate all of them:

Legis Cantio Quos legent mature censunto Profanum Vulgus Inscium Attrectado Omnes Astrologi Blennis Procul sunto aliter facit rite Sacer esto

from the word lex, in english law. or according to the law. poem. Nostradamus being a physician, legis cantio could mean that has to be written according to the law. So, here it stands for prescription, 'doctor's prescription!' translated as those who. comes from the verb legare which means, to read, to read attentively, to cast one's eyes over sth. means just right, timely. from the verb censeo, is translated as to judge, to think layman, uninitiated. common people. ignorant from the verb adtrecto means to try to understand, consider all astrologers, (greek), simpleton. adverb that means far. third person plural of the verb to be. means differently, otherwise. from the verb facere, third person singular of to make,to form, to do, to perform. according to customs or as they say. latin expression that means Be cursed! A modern translation would be Go and get stuffed!

Interprétation

A 'prescription' agaisnt stupid critics.

May those who read these verses think about this:
Even though laymen and ignorant people will deny it,
Astrologers are far from being uneducated or simpleton.
Those who think otherwise, go and get stuffed!