2/58-59 — The word that was changed
"We said, 'Enter this town, eat freely from where you wish, enter the gate bowing low and say "ḥiṭṭa", and We shall forgive you your faults.' But those who did wrong changed the word said to them for another word."
حِطَّة (ḥiṭṭa) — root ḥ-ṭ-ṭ: to bring down, to set low, to unload a burden. The word is a request for forgiveness in the sense of "take down our load, let our sin fall". The same root is used for the lowering of a price.
The command has two parts, and both convey lowering: entering bent low (the body) and saying ḥiṭṭa (the tongue). The one thing asked is that there be no arrogance at the moment of entry.
The verse recounts what was done in a very narrow expression: "they changed the word said to them for another word." What they said is not stated — the only thing stated is that another word was put in place of the word given.
Why this should be counted so heavy an offence may not be clear at first sight. But the mechanism is familiar: to refuse an obligation openly is costly — you cross over to the other side. To keep the formula and empty it out instead is costless: an onlooker sees that it has been complied with, and the one complying has not complied.
This is of the same family as the talbīs of verse 42 of the sūra — there falsehood was dressed in the garment of truth, here the appearance of compliance with a command is set up. In neither is there any need to lie; the form is preserved, the function is cancelled.