Expression "None are so blind as those that will not see"

[Moduis]

English Language Tests, Intermediate level

ESL/EFL Test #404 "English Slang Idioms (139)", question 2

"I tried to explain to him that he will lose everything he owns by borrowing huge sums to gamble with but none are so ......... as those who will not see," Jake told Lewis.

(a) distorted
(b) unfocused
(c) lame
(d) blind

English Language Tests, Intermediate level

ESL/EFL Test #404 "English Slang Idioms (139)", answer 2

"I tried to explain to him that he will lose everything he owns by borrowing huge sums to gamble with but none are so blind as those who will not see," Jake told Lewis.

Correct answer: (d) blind
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exlplain, please.

Moduis

[Mister Micawber]

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[4.] It is the amazing folly of multitudes that enjoy the means of grace, and it will be of fatal consequence to them, that they do not improve the day of their opportunities. The things of their peace are revealed to them, but are not minded or regarded by them; they hide their eyes from them, as if they were not worth taking notice of. They are not aware of the accepted time and the day of salvation, and to let it slip and perish through mere carelessness. None are so blind as those that will not see; nor have any the things of their peace more certainly hidden from their eyes than those that turn their back upon them.
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Native English teacher at Mister Micawber's

[Lost_Soul]

Hi, MM

What does "to improve the day of their opportunities" mean? I know it's a quote from the Bible, but figuring it out is beyond me...

Thanks !

[Mister Micawber]

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Hi LS,

This is not from the Bible, but from, I think, an exegesis. 'None are so blind...' is apocryphal. As for 'day of their opportunities', I think it just means 'chances'.
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Native English teacher at Mister Micawber's