I would suggest, without sources, that it's a midpoint of a development of an idiom that involves a preposition which are fickle linguistic artifacts. For instance, 'to the morrow' became 'to-morrow' and now neither form is common as they have been replaced by tomorrow. Thus, an adverbial prepositional phrase became an adverb. My speculation is that 'in the Hebrew tounge' would very easily become 'in the Hebrew' as an elliptical construction which would be shortened to 'in Hebrew'. Milton, after all, is hardly contemporary, and discussion of Hebrew in connection with the Bible would reflect older usage anyway out of a sense of continuity and devotion to the preservation of a linguistic culture in his contemporary religious experience. I mean, churches to this day, still read passages of English that use the archaic personal second person 'thou', 'thy', and 'thine' despite its expiration in early Modern English. On StackExchange philosophy, there's a Greek contributor who for months was posting in English using thou and thine, which shows the power of older forms of language to persist in strange and limited niches. I know a couple of songs with 'fare thee well', for instance because poets and lyricists are attracted to the power of archaic expression as a way to evoke feelings. So, semantically, there's no real difference in the literal meaning; it's just a psycholinguistic trait to be economical with syllables.