“Passages du Nouveau Testament” is perfect, there is no reason to look for another translation. It is very common to leave out the article in titles of books, articles, chapters, etc. if they describe what follows:

Some examples of titles or headers you may find:

“Guide de voyage: balades à Paris”

“Précis de mathématiques”

“Atlas historique”

“Petites annonces”

“Questions et réponses”

“Extraits choisis”

“Politique intérieure”

Look in point 4 of this article, I believe it gives quite a good practical rule for these cases where the article can be omitted: http://languagelearningbase.com/56021/omission-de-larticle

“Quelques passages du Nouveau Testament” would be acceptable, but the nuance I feel is that it stresses it would just be a short collection of a couple of passages, taken here and there.

“Certains passages du Nouveau Testament” sounds a bit odd (and I couldn’t explain why exactly… it’s just something a native speaker would not put as a title. Maybe because “certains” means these are very specifically chosen)