Bar lines in mensural notation (request for interpretation)

[Dan Eble]

Everything I know about 16th-Century Italian I learned from 20th-Century 
Spanish.  I hope that someone here is able and willing to check my guesses 
about this.

The following text seems to follow an introduction to mensural rests, and it 
surrounds a figure of a single bar line and a double bar line on an otherwise 
empty staff.  The book often uses bar lines in a way that looks semantically 
modern, though it also contains sample compositions without bar lines.

> Gli Ecclesiastici etiandio pongono le Pause ne i loro canti, no gia per 
> ornamento, ma per necessità. . . .
> Il che fa dibisogno, che li Compositori etiandio auertitenza delle parole si 
> oda, & intenda interamente: percioche facendo in cotal modo, allora si potrà 
> dire, che le Pause siano state poste nelle parti della cantilena con qualche 
> proposito, & non a caso.  Ne si debbeno porre per alcun modo, auanti che sia 
> finita la sentenza, cioè nel mezo della Clausula: conciosia che colui, che le 
> ponesse a cotal modo, dimostrarebbe veramente essere vna pecora, vn goffo, & 
> vno ignorante.  Però adunque il Musico si sforzerà di non cascare in simili 
> errori; accioche non dia alli dotti mala opinione di se, il che molto si 
> debbe prezzare, & preporre ad ogn'altra cosa.

This is what I've drawn out: When notating a chant, anyone who places 
full-height single or double lines anywhere but the end of a phrase is a sheep, 
a klutz, and an ignoramus.

My main doubt is whether this restriction is limited to church music.  I hope 
to understand whether to regard the bar lines in the rest of the book as a 
normal part of the notation that this author is teaching, or rather as a 
learning aid that he expects the reader not to carry over into his work.

More context might be required.  The book is available at IMSLP.  See page 212.
https://imslp.org/wiki/Le_Istitutioni_Harmoniche_(Zarlino,_Gioseffo)

Thanks and regards,
— 
Dan