Why are comparative adjectives used here, with the definite article? "...a hatred, the deeper for being concealed..."

In this sentence, the article 'the' precedes several comparative adjectives: 'deeper', 'bitter', 'greater', and 'stronger'. Now, for context, this sentence is the beginning of a text, and the adjectives are not compared with anything.

Terry soon became jealous of Sabina, and this rivalry turned at last to a hatred, the deeper for being concealed, and the more bitter in that he knew she had the greater power and the stronger will.

My question is: Why are the comparative forms of the adjective used when there is no comparison (and no, there is no 'implied' comparison to my knowledge), and why does the definite article precede them? I am aware that there are similar constructions to this (I believe they are called 'comparative correlatives'):

The sooner, the better.

The more one eats, the larger one will get.

The faster we run, the sooner we will get there.

However, in most of these, there is a comparison. Here, there are not any comparisons (and, before someone in the comments yells 'Context! Context!', there is no implied comparison available from the context). Is this a special use of the comparative adjective?

Solution 1:

The OED has an entry for this use of the:

a. Used with a following comparative adjective or adverb to emphasize the effect of circumstances indicated by the context.The circumstances are sometimes expressed by a phrase introduced by for, e.g. he is much the better for it, he looks the better for his holiday.

1724 Modest Def. Publick Stews 51 She will be the easier bribed, when Love and Avarice jointly must be gratified.

1782 W. Cowper Mutual Forbearance in Poems 24 Your fav'rite horse Will never look one hair the worse.

1838 J. Ruskin Ess. Music & Painting §24, in Wks. (1903) I. 285
And if others do not follow their example,—the more fools they.

1883 Law Times 27 Oct. 425/1 What student is the better for mastering these futile distinctions?

1938 Manch. Guardian 8 Mar. 8/1 This record is the more remarkable when we remember the defective eyesight by which..Dr. Garvie has been handicapped.

2014 K. Fforde Christmas Feast 289 She wouldn't really be any the wiser.

There is also a discussion of this in the Cambridge Grammar of the English Language p1131-1132

i This didn’t make her achievement [any the less significant].

ii In the Swedish context, notable for its tradition of peace and non-violence, the senseless futility of this act stands out [the more starkly].

iii The plight of the four British employees greatly perturbed Urquhart, [the more] because a request to the Governor for a contingent of Cossacks to escort them to safety had been turned down.

iv The result is [all the more disappointing] because she had put in so much effort.

v That’s [all the more reason to avoid precipitous action].

vi He went prone on his stomach, [the better] to pursue his examination.

The here modifies the following comparative (more, less, better), forming a phrase which in turn is modifier to an adjective ([i/iv]), an adverb ([ii]), a verb ([iii/vi]) or determiner to a nominal ([v]). In [i-ii] the is freely omissible. In [iii] the underlined occurrence of the would be omissible if it introduced a modifier rather than a supplement (which would mean dropping the comma), but not as it stands. In [iv], all the might be glossed as “even”, or all the+ comparative as “especially”; the can only be omitted if all is omitted too. Example [v] is similar, except that all the more is here a DP functioning as determiner in NP structure. In [vi] the better is a fronted modifier in the infinitival clause of purpose; the is obligatory in this position but optional in the basic position - compare in order to pursue his examination (the) better.

The is completely excluded if the secondary term is expressed: *The result was the better than I had expected. Nor is the permitted when the secondary term is recoverable anaphorically, from what has gone before. We cannot, for example, insert the in It was cloudy and cold for the first two days but on the third day the weather was better, where we understand “better than on the first two days”.

Solution 2:

It's a literary usage, with as @Lawrence says an implicit comparison. Compare

• "How are you, Kerry?" ... "All the better for seeing you."

You can easily fill in the deletion / adjustment here:

• ... "All the better than would have been the case had I not seen you."

It's good to have the pithier, more punchy alternative.

So

• ' ... deeper than it would have been if it had not been concealed' /
• ' ... [even] more bitter than would have been the case had he not known she had the greater power and the stronger will'.