The phrase "that theirs are gardens beneath which rivers flow (anna la-hum jannâtin tajrî min tahtihâ al-anhâr):"

Consider all the parts of this phrase: the confirmative "anna - that," the specifying "lam" [of "theirs (la-hum)]," the precedence of "la-hum -theirs," the plural "gardens (jannât)" and its being indefinite and the mention of the flowing waters, the mention of "min" and "taht - beneath," the specifying [the plural] of "rivers (anhâr)" and its being definite; - like moisture trickling from all sides of the dry earth into a central pool, all these parts assist and respond to each other reinforcing the main aim, which is joy, pleasure, and requital.

[To explain:] "That (anna)" indicates that since the mind might be hesitant about the stupendousness of the thing about which the good news is given, it needs to be corroborated. Also, it is characteristic of a context (maqâm) [inducing] joy that it repels ungrounded fears, for the least anxiety shatters the imagining and chases away the joy. It is also a sign that this is not a mere promise but an actual reality.

The "lam" of "la-hum - theirs" indicates particularity, ownership, and entitlement, [meaning that the thing about which good news is given] is exclusive [to the believers], and is theirs, and that they are deserving of it, which perfects [their] pleasure and augments [their] joy. Otherwise it would be like a king entertaining a pauper.

The precedence of "theirs (la-hum)" indicates that among the people it is [the believers] who are singled out for Paradise. [As a result], they observe the situation of the people of Hell, which will make apparent the value of paradisical pleasure.

The plural of "gardens (jannât)" indicates the [great] number of gardens or paradises and their various degrees proportionate to the [many] various degrees of actions. It is a sign too that every part of Paradise is a paradise, and infers also that whatever portion is allotted to a person, with its great extent it will seem like the whole of Paradise; [individuals] will not be herded together with their group [or community] to a [particular] place.