Allah condemns the idolators for worshipping others instead of Allah with no evidence or proof for doing so.
(Or have We given them any Book before this) means, before their idolatry.
(to which they are holding fast) means, with regard to what they are doing. This is not the case. This is like the Ayah:
(Or have We revealed to them an authority (a Scripture), which speaks of that which they have been associating with Him) (30:35) meaning, that did not happen. Then Allah says:
(Nay! They say: "we found our fathers following a certain way and religion (Ummah), and we guide ourselves by their footsteps.") meaning, they have no grounds for their belief in idolatry apart from the fact that they are imitating their fathers and forefathers who were following a certain Ummah or way, i.e., religion. The word Ummah is used in a similar manner elsewhere, where Allah says:
(And verily, this your religion (Ummah) is one religion) (23:52), and they said;
(and we by their footsteps) means, behind them
(We guide ourselves) This is their claim with no evidence. Then Allah points out that what these people say was already said by those who were like them among the nations of the past who disbelieved in the Messengers. Their hearts and their words are similar.
(Likewise, no Messenger came to those before them but they said: "A sorcerer or a madman!" Have they transmitted this saying to these Nay, they are themselves a people transgressing beyond bounds!) (51:52-53) And Allah says here:
(And similarly, We sent not a warner before you to any town (people) but the luxurious ones among them said: "We found our fathers following a certain way and religion, and we will indeed follow their footsteps.") Then He says:
(Say) -- `O Muhammad, to these idolators --'
("Even if I bring you better guidance than that which you found your fathers following" They said: "Verily, we disbelieve in that with which you have been sent.") `Even if they were convinced of the truth of what you have brought to them, they will not follow it, because of their evil intentions and their arrogance towards the truth and its people.'
(So We took revenge on them) means, on the disbelieving nations, by inflicting various kinds of punishments, as Allah has described in the stories of those nations.
(then see what was the end of those who denied) means, see what became of them, how they were destroyed and how Allah saved the believers.