ولو أن للذين ظلموا
And those who did wrong, (means, the idolators).
ما في اﻻرض جميعا ومثله معه
if they had all that is in earth and therewith as much again,
ﻻفتدوا به من سوء العذاب
they verily, would offer it to ransom themselves therewith from the evil torment;
means, that which Allah has decreed for them on the Day of Resurrection. But the ransom will not be accepted from them, even if it were to be an earth-full of gold as He mentioned elsewhere (3:91).
يوم القيامة
on the Day of Resurrection,
Then Allah says:
وبدا لهم من الله ما لم يكونوا يحتسبون
and there will become apparent to them from Allah what they had not been reckoning.
which means, when they come to realize what Allah's punishment for them will be, which they had never before imagined