(Then, after them, We created other generations.) meaning, nations and peoples.
(No nation can advance their term, nor can they delay it.) means, they are taken at the appropriate time, as decreed by Allah in His Book that is preserved with Him, before they were created, nation after nation, century after century, generation after generation, successors after predecessors.
(Then We sent Our Messengers in succession.) Ibn `Abbas said, "(This means) following one another in succession." This is like the Ayah:
(And verily, We have sent among every Ummah a Messenger (proclaiming): "Worship Allah, and avoid Taghut (all false deities)." Then of them were some whom Allah guided and of them were some upon whom the straying was justified) 16:36.
(Every time there came to a nation their Messenger, they denied him;) meaning the greater majority of them. This is like the Ayah:
(Alas for mankind! There never came a Messenger to them but they used to mock at him.) 36:30
(so We made them follow one another,) means, `We destroyed them,' as Allah says:
(And how many generations have We destroyed after Nuh!) 17:17
(and We made them as Ahadith) meaning, stories and lessons for mankind, as Allah says elsewhere:
(so, We made them as tales (in the land), and We dispersed them all totally) 34:19.