means, they do good deeds sincerely for the sake of Allah, and they obey Allah, doing what Allah has prescribed for them. Ibn Jarir recorded that Sa'id bin 'Imran said, "I read this Ayah to Abu Bakr As-Siddiq, may Allah be pleased with him:

He said, 'Those are the ones who do not associate anything with Allah.'" Then he reported a narration of Al-Aswad bin Hilal, who said, "Abu Bakr As-Siddiq, may Allah be pleased with him, said, 'What do you say about this Ayah:

{Verily, those who say: "Our Lord is Allah," and then they stand firm,}?' They said:

'They shun sin.' He said, 'You have not interpreted it improperly.' They say: 'Our Lord is Allah, then they stand firm and do not turn to any other god besides Him.'" This was also the view of Mujahid, 'Ikrimah, As-Suddi and others. Ahmad recorded that Sufyan bin 'Abdullah Ath-Thaqafi said, "I said, 'O Messenger of Allah, tell me something that I can adhere to.' He said:

«Say, my Lord is Allah, then stand firm.» I said, 'O Messenger of Allah, what do you fear most for me?' The Messenger of Allah took hold of the edge of his tongue and said,

«This is.»" This was also recorded by At-Tirmidhi and Ibn Majah; At-Tirmidhi said, "Hasan Sahih."
Muslim also recorded it in his Sahih, and An-Nasa'i recorded that Sufyan bin 'Abdullah Ath-Thaqafi said, "I said, 'O Messenger of Allah, tell me something about Islam that I will not have to ask anyone about it after you.' He said:

«Say: I believe in Allah, then stand firm.» - then he mentioned the rest of the Hadith.

{on them the angels will descend}. Mujahid, As-Suddi, Zayd bin Aslam and his (Zayd's) son said, "This means, at the time of death, and they will say,

{Fear not}." Mujahid, 'Ikrimah and Zayd bin Aslam said, "This means not to fear "that which you will face in the Hereafter."

{nor grieve!} 'for what you have left behind of worldly things, children, family, wealth and debt, for we will take care of it for you.'

So they give glad tidings of the end of bad things and the arrival of good things. This is like what is said in the Hadith narrated by Al-Bara', may Allah be pleased with him:

«The angels say to the soul of the believer, "Come out, O good soul from the good body in which you used to dwell, come out to rest, and provision and a Lord Who is not angry."»