Allah says, informing about the response of Nuh to his people,
(Tell me, if I have a clear proof from my Lord,) Bayyinah means certainty, a clear matter, and truthful prophethood. That is the greatest mercy from Allah upon him (Nuh) and them (his people).
(but that (mercy) has been obscured from your sight.) "Obscured from your sight" in this verse means, `it was hidden from you and you are not guided to it. Thus, you people did not know its importance so you hastily rejected and denied it.'
(Shall we compel you (to accept) it) This means, "Should we force you to accept it, while you actually detest it."