In verse 52, it was said: قَالُوا يَا وَيْلَنَا مَن بَعَثَنَا مِن مَّرْقَدِنَا (They will say, "Woe to us! Who has raised us from our sleeping place?" ). Though the disbelievers were already having their punishment in their graves with no sign of any relief, yet this punishment will appear as nothing when compared with the punishing circumstances of the day of Qiyamah, therefore, they will cry out as to why they had to be taken out of their graves, for it would have been better if they had stayed right there. A response to this will come from either the angels or the common believers.
This response appears immediately next in verse 52: هَـٰذَا مَا وَعَدَ الرَّحْمَـٰنُ وَصَدَقَ الْمُرْسَلُونَ ("This is what the Rahman had promised, and the messengers had told the truth.) - to which they paid no attention. At this place, a choice has been made in using the word: رَّحْمَـٰنُ (Rahman: The Most Merciful) out of the many attributes of Allah. It serves as an indicator - as for Him, He had already made elaborate arrangements, in His mercy, that you remain safe from this punishment, and that His act of alerting you in advance through His promise and through His Books and Prophets was, in fact, but a dictate of His attribute of mercy.