Commentary on Tafsir al-Jalalayn: ((They are served)) to each of them ((with a cup)) which is the vessel with its drink ((from a spring)) of wine that flows on the surface

Some of them do not see the back of another on thrones, the plural of throne, which are the seats upon which they sit, but they are not like the thrones of this world, rather they are carved from gold. You cannot imagine the beauty of these images, for they contain what no eye has seen, no ear has heard, and what has not occurred to the heart of any human being. What has not occurred to the heart of a human being cannot be imagined by him, for it is beyond what can be imagined. Everything you estimate of pleasure and beauty, Paradise is higher and greater. And His saying is a state of the pronoun attached to His saying "on thrones," meaning in the state of them being facing one another. This indicates the perfection of their manners and the spaciousness of their seating. The perfection of manners and the spaciousness of seating, the perfection of manners, because they are facing one another and none of them turns his back to the other. It also indicates the spaciousness of the seating, because if they are many and become facing one another, the circle must be wide. Thus, the seating is spacious; however many people come, it accommodates them and they face one another in it. He says, "Some of them do not see the back of another," for the sake of facing one another.
"To each of them

with a cup

بكأس

is the vessel with its drink

from a spring

من معين

of wine that flows on the surface of the earth like rivers of water". They are served. "They are served" is a present tense verb for the unknown agent, and it is not mentioned who serves them, but it is mentioned in another verse that it is young boys, meaning small boys. If you see them, you would think them scattered pearls, due to their beauty and their loveliness. "Scattered" because of their distribution in serving their masters. When pearls are scattered, they are strewn on the ground, so they are strewn in serving their masters, each having a task. This delights a person to find these boys, each in his specific service, with none idle and none waiting for the other, unlike the boys of this world who jostle, each saying, "Let me go until it is my turn." No, each is in a specific service. This is the most delightful thing for the master when he sees these boys attending to their service in this manner.
And His saying , the author said, "is the vessel with its drink". The cup is well known, and it is the vessel with its drink. Allah the Exalted has clarified that this cup is full , meaning filled. And yet, it is filled to a known measure; it is not large and filling, such that if a person drinks it, he becomes tired, and if he leaves a remainder, it becomes unappetizing. Nor is it small such that it does not quench their thirst, for they do not become thirsty, but rather for pleasure. Rather, Allah the Exalted said , meaning it is made to the measure by which the drinker takes pleasure, neither large nor small.
And His saying , he said, "of wine that flows on the earth". A spring, in its original meaning, is flowing water, and what is meant here by "a cup from a spring" is from a spring of wine, like a spring of water that flows. Allah the Exalted has clarified in Surat al-Qital [Muhammad:15] rivers that flow. He who created it, Mighty and Majestic, from this creature that resembles a fly, is capable of creating these large quantities of honey. He is capable of creating rivers of honey in Paradise, and this is not strange. These rivers do not come from bees, but they come by the command of Allah, "Be, and it is." Filtered honey, with no wax or impurities, of the best in richness, taste, and scent. And Ibn al-Qayyim said in al-Nuniyyah, based on a hadith that came regarding this:
"Its rivers flow without a channel, Glory to the One who holds them back from overflowing"
Meaning, they are not like the rivers of this world that require a channel, boundaries that prevent them from going right and left, or a trench dug for the river. No, they flow on the surface of the earth according to what their people desire, without workers directing them, digging, or establishing them, but they flow as they wish without effort. He said, "Glory to the One who holds them back from overflowing". And He who held back the sea from drowning the people of the earth—is that not a thing for Paradise? He is capable of holding back these rivers so they do not deviate to the right or to the left.