Tafsir of Luqman 31:8

(Indeed, those who have believed and done righteous deeds) is an exposition of the state of those who believe in His verses, the Exalted, following the exposition of the state of those who disbelieve in them. That is, those who believed in His verses, the Exalted, and acted according to their requirements.

(For them)—as a consequence of what was mentioned of their faith and their deeds—(are gardens of bliss), meaning abundant bliss. The addition of "gardens" to "bliss" is in the sense of the gardens being inclusive of it, similar to your saying: "books of jurisprudence."

In this, there is an indication that they possess this bliss by way of intrinsic proof, which is more eloquent than saying "they have the bliss of the gardens," for the latter does not necessitate that the gardens themselves are their property; a person might enjoy something without owning it. It has been said regarding why it is more eloquent: it is because the bliss is made the foundation within them, by which the gardens are distinguished, thereby conveying the abundance and renown of the bliss. Regardless, "gardens of bliss" are the well-known gardens.

Ibn Abi Hatim recorded from Malik ibn Dinar that he said: "The gardens of bliss are between the gardens of Firdaws and the gardens of ‘Adn, and in them are maidens created from the roses of Paradise." It was said: "And who shall dwell in them?" He replied: "Those who intended to commit sins, but when they remembered My majesty, they remained mindful of Me; and those whose loins bent in My fear." And Allah, the Exalted, knows best the authenticity of the report.

The sentence contains two [possible] predicates. It is said that the better view is to make "(for them)" the predicate, and "(gardens of bliss)" elevated by it as the subject [acting in the place of a subject].