Could you please interpret the verse 5:85 of the Quran? What does it mean?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

Allah says (what means): {So Allah rewarded them for what they said with gardens [in Paradise] beneath which rivers flow, wherein they abide eternally. And that is the reward of doers of good.} [Quran 5:85]

Ibn Katheer said:

“{So Allah rewarded them for what they said with gardens [in Paradise] beneath which rivers flow}; meaning that He rewarded them for embracing the faith and recognizing and believing in the truth {with gardens [in Paradise] beneath which rivers flow}; and they will never be removed from it, for they will dwell and remain in it forever and ever. {Such is the reward of good-doers}; meaning because of following the truth and obeying it wherever, whenever, and with whomever they find it…” 

What is meant by those who are rewarded in the verse are the Christians who believed in the Prophet and they are those who were mentioned in the saying of Allah (which means): {That is because among them are priests and monks and because they are not arrogant. And when they hear what has been revealed to the Messenger, you see their eyes overflowing with tears because of what they have recognized of the truth. They say, "Our Lord, we have believed, so register us among the witnesses. And why should we not believe in Allah and what has come to us of the truth? And we aspire that our Lord will admit us [to Paradise] with the righteous people." So Allah rewarded them for what they said with gardens [in Paradise] beneath which rivers flow, wherein they abide eternally. And that is the reward of doers of good. But those who disbelieved and denied Our signs - they are the companions of Hellfire.} [Quran 5:82-86]

Ibn Katheer said:

“The saying of Allah: {This is because they are priests and monks and that they are not arrogant.}; this describes them with knowledge, worship and humbleness, along with following the truth and fairness. Then Allah says (what means) {And when they hear what has been revealed to the Messenger, you see their eyes overflowing with tears because of what they have recognized of the truth.}; this refers to the good news that they had about Muhammad ; that he would be sent as a Prophet. {They say: Our Lord, we have believed, so register us among the witnesses} who testify to the truth and believe in it."

An-Nasaa’i reported from ‘Amr ibn ‘Ali Al-Fallaas, from ‘Umar ibn ‘Ali ibn Muqaddam, from Hishaam ibn ‘Urwah, from his father, from ‘Abdullah ibn Az-Zubayr, that:

“This verse was revealed about An-Najaashi (Negus, King of Abyssinia) and his companions: {And when they hear what has been revealed to the Messenger, you see their eyes overflowing with tears because of what they have recognized of the truth.} … They were the Christians who were mentioned in the verse (which means) {And indeed, among the People of the Scripture are those who believe in Allah and what was revealed to you and what was revealed to them, [being] humbly submissive to Allah. They do not exchange the verses of Allah for a small price. Those will have their reward with their Lord. Indeed, Allah is swift in account.} [Quran 3:199] They are those about whom Allah says (what means) {Those to whom We gave the Scripture before it - they are believers in it. And when it is recited to them, they say, "We have believed in it; indeed, it is the truth from our Lord. Indeed we were, [even] before it, Muslims [submitting to Allah]." Those will be given their reward twice for what they patiently endured and [because] they avert evil through good, and from what We have provided them they spend. And when they hear ill speech, they turn away from it and say, "For us are our deeds, and for you are your deeds. Peace will be upon you; we seek not the ignorant."} [Quran 28:52-55] It is for this reason that Allah says here (what means) {So Allah rewarded them for what they said with gardens [in Paradise] beneath which rivers flow} [Quran 5:85]; meaning that He rewarded them for embracing the faith and recognizing and believing in the truth {with gardens [in Paradise] beneath which rivers flow} and they will never be removed from it, for they will dwell and remain in it forever and ever. {Such is the reward of good-doers}; meaning because of following the truth and obeying it wherever, whenever, and with whomever they find it…”

Allah knows best.