Why is a cuckolded husband “fit for heaven” in Byron's Don Juan?

Question

Canto 5, stanza 154, from Byron's Don Juan:

His majesty saluted his fourth spouse
     With all the ceremonies of his rank,
Who clear'd her sparkling eyes and smooth'd her brows,
     As suits a matron who has play'd a prank;
These must seem doubly mindful of their vows,
     To save the credit of their breaking bank:
To no men are such cordial greetings given
As those whose wives have made them fit for heaven.

What is the meaning of made them fit for heaven?

Why would a cuckolded husband be "fit for heaven"?

(According to the plot, "his majesty" is a sultan who has been cuckolded by one of his wives: she ordered Don Juan bought on the slave market and brought to her in female disguise)

Answer 1

I don't know how it originated, but the idea that cuckolds go to heaven is apparently an old English proverb/saying, not one that was invented by Byron. A Dictionary of Sexual Language and Imagery in Shakespearean and Stuart Literature, by Gordon Williams, gives a number of similar examples in the entry for "Cuckolds are Christians":

Tilley has 'In rain and sunshine cuckolds go to heaven' (R12; the thought occurs from 1591, but this form is cited from 1659). The simplified "Cuckolds go to Heaven' occurs in Spinke, Quackery Unmask'd (1711) 8; and Leanerd, Rambling Justice (1678) Epil. declares: 'both Fools and Cuckolds go to Heaven'.

(p. 342)