This question pertains to the following ayat:
And it is He who has made you successors upon the earth and has raised some of you above others in degrees [of rank] that He may try you through what He has given you. Indeed, your Lord is swift in penalty; but indeed, He is Forgiving and Merciful.
And [mention] when your Lord declared that He would surely [continue to] send upon them until the Day of Resurrection those who would afflict them with the worst torment. Indeed, your Lord is swift in penalty; but indeed, He is Forgiving and Merciful.
There may be other similar ayat that I haven't cited.
If I understand correctly, the first ayah above is in the context of the Prophet Muhammad, and generally applies to all people. The second ayah is in the context of the people of Prophet Moses, some of whom were transformed into apes as a punishment (Qur'an 7:166), where indeed the penalty was immediate (i.e., prior to the the Day of Judgment).
I'm not clear on what it means to be "swift in penalty" here. For Allah, notions of time (and thus what it means to be "swift") may be radically different to human notions of time. Also, after becoming deceased, we may not experience time at all.
Question: What does Allah being "swift in penalty" mean to today's Muslims?