Here Allah tells us about the blessed believers, who will be taken to Paradise in groups, one group after another, starting with the best of them: those who are closest to Allah, then the most righteous, then the next best and the next best. Each group will be with others like them, Prophets with Prophets, the true believers with their peers, the martyrs with their counterparts, the scholars with their colleagues, every group composed of people of the same kind.
{till when they reach it,} means, when they arrive at the gates of Paradise, after passing over the Sirat, where they will be detained on a bridge between Paradise and Hell, and any injustices that existed between them in this world will be settled until they have all been purified from sin through this trial. Then permission will be granted for them to enter Paradise.
It was recorded in the Hadith about the Trumpet that when the believers reach the gates of Paradise, they will consult one another as to who should ask permission for them to enter. They will ask Adam, then Nuh, then Ibrahim, then Musa, then 'Isa, then Muhammad (may blessings and peace be upon them all). This is akin to what will happen in the arena of judgement, when they will ask for someone to intercede for them with Allah when He comes to pass judgement. This is to show the noble position of Muhammad above the rest of mankind in all situations.
In Sahih Muslim, it is reported that Anas, may Allah be pleased with him, said, “The Messenger of Allah said: ... heart. They will glorify Allah morning and evening.»” This was also recorded by Al-Bukhari and Muslim. Al-Hafiz Abu Ya'la recorded that Abu Hurayrah, may Allah be pleased with him, said, “The Messenger of Allah said: «The first group to enter Paradise will look like the moon on the night when it is full. They will be followed by a group which looks like the brightest star shining in the sky. They will not urinate or defecate or spit or blow their noses. Their combs will be of gold, their sweat will be musk and their censers will be of aloeswood. Their wives will be Al-Hur Al-'Iyn, and they will all look the same, as if they are one person in the image of their father Adam, sixty cubits tall.»” They [Al-Bukhari and Muslim] also produced this from the Hadith of Jabir. It was reported that Abu Hurayrah, may Allah be pleased with him, said, “The Messenger of Allah said: «A group of my Ummah, seventy thousand, will enter Paradise with faces shining like the moon on the night when it is full.» 'Ukkashah bin Mihsan stood up and said, ‘O Messenger of Allah, pray to Allah to make me one of them.’ He said, «O Allah, make him one of them.» Then one of the Ansar stood up and said, ‘O Messenger of Allah, pray to Allah to make me one of them.’ He said, «'Ukkashah has beaten you to it.»” This was recorded by (Al-Bukhari and Muslim). This Hadith - about the seventy thousand who will enter Paradise without being brought to account - was also recorded by Al-Bukhari and Muslim from Ibn ‘Abbas, may Allah be pleased with him, Jabir bin ‘Abdullah, 'Imran bin Husayn, Ibn Mas'ud, Rifa'ah bin ‘Arabah Al-Juhani and Umm Qays bint Mihsan - may Allah be pleased with them all - and also from Abu Hazim from Sahl bin Sa‘d, may Allah be pleased with them, who said that the Messenger of Allah said: «Seventy thousand or seven hundred thousand of my Ummah will surely enter Paradise, holding on to one another, such that the first and last of them will enter Paradise together, with their faces looking like the moon on the night when it is full.»
{till when they reach it, and its gates will be opened and its keepers will say: "Salam ‘Alaykum (peace be upon you)! You have done well, so enter here to abide therein forever."} This is a conditional sentence that is not complete. What it implies is that when they come to the gates of Paradise the gates will be opened for them as a sign of honor, and the angelic gatekeepers will meet them with glad tidings, greetings of peace and praise. Unlike the gatekeepers of Hell who will meet the disbelievers with rebuke and reprimand, the believers will be filled with happiness and joy, each according to his degree of luxury and delights. What happens after this is not mentioned; it is left for the imagination to think of its dearest wishes and be filled with hope. It is known from the Sahih Hadiths that Paradise has eight gates. Imam Ahmad recorded that Abu Hurayrah, may Allah be pleased with him, said, “The Messenger of Allah said: «Whoever spends a pair of something from his wealth for the sake of Allah, will be called from the gates of Paradise. Paradise has (several) gates. Whoever is among the people of prayer, will be called from the gate of Prayer; whoever is among the people of charity, will be called from the gate of Charity; whoever is among the people of Jihad, will be called from the gate of Jihad; whoever is among the people of fasting, will be called from the Gate of Ar-Rayyan.» Abu Bakr said, ‘O Messenger of Allah, it does not matter from which gate one is called, but will anyone be called from all of them?’ He said, «Yes, and I hope that you will be one of them.»” Something similar was also recorded by Al-Bukhari and Muslim. It was reported from Sahl bin Sa‘d, may Allah be pleased with him, that the Messenger of Allah said: «In Paradise there are eight gates; one of them is called Ar-Rayyan, and no one will enter it except those who fast.» In Sahih Muslim, it is recorded that 'Umar bin Al-Khattab, may Allah be pleased with him, said, “The Messenger of Allah said: ... them that the distance between the two gateposts of Paradise was the distance of a forty-year journey, but there would come a day when they would be packed with crowds of people.” Allah says, {and its keepers will say: "Salam ‘Alaykum (peace be upon you)! You have done well,"} meaning, ‘your deeds and words were good, and your efforts were good, and your reward is good.’ The Messenger of Allah issued commands during some of his military campaigns that it should be shouted out to the Muslims: «No one enters Paradise except a Muslim soul,» or, according to one report, «A believing soul.» Allah says, {so enter here to abide therein forever.} means, to dwell therein, never seeking any change. {And they will say: "All the praises and thanks be to Allah Who has fulfilled His promise to us..."} means, when the believers see the great reward and splendors, blessing and grand generosity, they will say, {All the praises and thanks be to Allah Who has fulfilled His promise to us} meaning, ‘the promise which He made to us through His Messengers who called us to this in the world.’ {Our Lord! Grant us what You promised unto us through...