quam laeta sit

[Can I Try?]

I would be grateful for comments on my translation. Is sit here subjunctive because it is in a subordinate clause?

Non advertunt aut capiunt quam laeta sit, quam salubris et expedita
et ex bona consuetudine quam facilis et jucunda reddatur devotorum
sobrietas qui cum Apostolo castigant corpus suum et in servitutem redigunt;

They don’t turn to, or take possession of, what is favorable, what is healthy—both expedient
and according to a good custom of the faithful, what is easy and agreeable;
sobriety is granted [to those] who, with the Apostle, chastises their body and brings it into subjection (I Cor 9:27);

 

[Laurentius]

I think it is an indirect interrogative.

 

[Pacifica]

I think it is an indirect interrogative.

It is (or, as it's more commonly called, an indirect question).

Here's a translation of the passage:

"They do not notice or grasp how happy, how wholesome and free from difficulty sobriety is, and how easy and pleasant it is made by good habit, for the devout who with the Apostle chastise their body and bring it into subjection."

Some substantial changes to the grammatical construction were needed to make the sentence work in English. Literally, it is "... how happy... [the sobriety of the devout who etc.] is and how easy and pleasant [the sobriety of the devout etc.] is made from good habit".